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B.C. Home » Ministry of Health » Vital Statistics Agency » Statistics and Reports » Quarterly Digest » Second Quarter of 1997

Quarterly Digest
Volume 7 - Number 2 October 1997

• Preface
  
  
• Map: B.C. Local Health Areas
  
  
• British Columbia: Local Health Areas (LHA) within Health Regions
  
  
• Vital Events Statistics
  (Population, Livebirth, Death, Marriage, Stillbirth, Infant Deaths)
  
  
• Selected Birth Statistics
  (Low Birthweight, Preterm, Teenage Mother, Elderly Gravida, Cesarean Section)
  
  
• External Causes of Death
  (Accidents - [Motor Vehicle Accidents, Poisoning, Falls Burns/Fire, Drowning, Other], Suicide, Homicide, Other External Causes)
  
  
• Neoplasm Deaths
  (Lung, Female Breast, Colorectal, Other G.I., Female Reproductive, Male Reproductive, Blood/Lymph, Other Malignancy, Nonmalignant and Unspecified)
  
  
• Heart Disease Deaths
  (Rheumatic/Valvular, Hypertension, Ischemic, Conductive & Dysrhythmic, Heart Failure, Congenital, Other)
  
  
• Other Selected Death Statistics
  (Respiratory Diseases - [Emphysema, COPD, Pneumonia/Influenza, Other], Diabetes, Alcohol-Related, AIDS, Cerebral and Other Vascular, Liver Disease)
  
  
• Summary Article:
  Women and cancer: Lung and breast cancer among women in B.C., 1974-1996
  by Z. Kashaninia
  
  
• Glossary
  
  
• Contributors' Note
  
  
• Readers' Note
  
  

Preface

This Quarterly’s standard tables of vital event statistical information focus on the second quarter of 1997 and, with year-to-date numbers, provide data for the first half of the current year. These are the most up-to-date British Columbia birth, death, marriage, and stillbirth statistics to be provided in publication.

To make Quarterly information more accessible and flexible, soon after hardcopy release, Quarterly Digest issues will continue to be made available at our web site, http://www.hlth.gov.bc.ca/vs.

Due to the fact that Vital Statistics Agency’s files are continually being updated, totals compiled by addition of the annual quarters will not correspond exactly to year-to-date and year-end figures. For the same reason, depending on the date the data are extracted, there will be differences in numbers presented in this year’s Quarterly Digests and those eventually reported in the Vital Statistics 1997 Annual Report. Therefore, the numbers provided in this report should be considered provisional. Finally, the usual cautions regarding random fluctuations in values, particularly those involving small numbers, must be noted.

In 1996, cancer was the leading cause of death of women in British Columbia. In that year, the 3,368 women who died of cancer accounted for more than one out of every four female deaths in the province. This issue’s feature article is the first of two that examine the impact of cancer on the women of British Columbia. After a brief overview of all cancer mortality among women, this article focuses on the two most frequently fatal cancers - of the lung and of the breast. For each of these cancers, numbers of deaths, national/provincial comparisons, differences by age and region, and changes over time are presented. This article also provides a brief summary of relevant information from external sources and studies related to incidence, smoking and lung cancer, and mammography.

Wherever possible, changes such as additional cause of death categories, percent, or year-to-date totals, have been added to the Quarterly Digest as requested by our readers. Suggestions for article topics or contributions are also welcome. Your support and input into this publication are greatly appreciated.

R.J. Danderfer	Soo-Hong Uh
Director	Manager
British Columbia	Information and Resource
Vital Statistics Agency	Management Branch
	Vital Statistics Agency

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British Columbia
Local Health Areas

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British Columbia:
Local Health Areas (LHA)
within Health Regions

01 East Kootenay LHA 01 Fernie 02 Cranbrook 03 Kimberley 04 Windermere 05 Creston 18 Golden 02 West Kootenay - Boundary LHA 06 Kootenay Lake 07 Nelson 09 Castlegar 10 Arrow Lakes 11 Trail 12 Grand Forks 13 Kettle Valley 03 North Okanagan LHA 19 Revelstoke 20 Salmon Arm 21 Armstrong-Spallumcheen 22 Vernon 78 Enderby 04 South Okanagan Similkameen LHA 14 Southern Okanagan 15 Penticton 16 Keremeos 17 Princeton 23 Central Okanagan 77 Summerland 05 Thompson LHA 24 Kamloops 26 North Thompson 29 Lillooet 30 South Cariboo 31 Merritt 06 Fraser Valley LHA 32 Hope 33 Chilliwack 34 Abbotsford 75 Mission 76 Aggassiz-Harrison 07 South Fraser Valley LHA 35 Langley 36 Surrey 37 Delta 08 Simon Fraser LHA 40 New Westminster 42 Maple Ridge 43 Coquitlam 09 Coast Garibaldi LHA 46 Sechelt 47 Powell River 48 Howe Sound

10 Central Vancouver Island LHA 65 Cowichan 66 Lake Cowichan 67 Ladysmith 68 Nanaimo 69 Qualicum 70 Alberni 11 Upper Island / Central Coast LHA 71 Courtenay 72 Campbell River 84 Vanouver Island West 85 Vancouver Island North 12 Cariboo LHA 27 Cariboo-Chilcotin 28 Quesnel 49 Central Coast 93 Eutsuk 13 North West LHA 50 Queen Charlotte 52 Prince Rupert 54 Smithers 80 Kitimat 87 Stikine 88 Terrace 92 Nishga 94 Telegraph Creek 14 Peace Liard LHA 59 Peace River South 60 Peace River North 81 Fort Nelson 15 Northern Interior LHA 55 Burns Lake 56 Nechako 57 Prince George 16 Vancouver LHA 39 Vancouver 17 Burnaby LHA 41 Burnaby 18 North Shore LHA 44 North Vancouver 45 West Vancouver-Bowen Island 19 Richmond LHA 38 Richmond 20 Capital LHA 61 Greater Victoria 62 Sooke 63 Saanich 64 Gulf Islands

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Women and cancer: Lung and breast cancer among women in B.C., 1974-1996

by Z. Kashaninia

I. Introduction and Overview

Cancer was the leading cause of death for women in British Columbia in 1996. In that year alone, 3,368 women died of cancer; that is, more than one out of every four female deaths in British Columbia was caused by cancer.

Figure 1
Proportion of All Deaths Among Females due to Cancer
by Age Group
British Columbia, 1996

Note: Percent of all female deaths due to cancer in the specified age groups.

In 1996, 53.1 percent of deaths among females aged 45-64 were due to cancer. The percentage of deaths caused by cancer were also notable at 31.4 percent for 25-44 and at 31 percent for the 65-84 age groups. Cancer was also responsible for 20.7 percent of deaths in the 1-14 age group.

Figure 2
Percent of Female Cancer Deaths as a
Proportion of All Female Deaths
British Columbia, 1975-1995

Note: Percent of all female deaths due to cancer in the specified years.

Over the past twenty years, the percentage of females who died of cancer steadily increased in British Columbia. Although, the percentage of those who died of cancer between 1990 and 1995 stayed the same at 27 percent, there was still a notable increase from 21 percent in 1975 and 23.7 percent in 1980.

Figure 3
Female Cancer Deaths
British Columbia, 1996

* Reproductive cancers include cervix, uterus, ovary and all other female genital parts.

In 1996, 26.5 percent of all female deaths in British Columbia were due to cancer. The most frequent female cancer deaths were due to lung cancer (24 percent) closely followed by breast cancer at 18 percent. Reproductive cancers accounted for the third highest female cancer deaths at 9 percent.

This paper will focus on the two major types of cancer deaths among women, namely, lung cancer and breast cancer from 1974-1996. Both of these cancers will be analyzed on a provincial and regional basis. An inter-provincial and national comparison will also be made to provide a context of B.C.’s female population’s incidence and mortality rates of lung and breast cancers.

 

Methodology

The British Columbia mortality data used in this report were obtained from the registrations and medical certifications of deaths submitted to the British Columbia Vital Statistics Agency. The underlying cause of death (UCOD) was coded to the International Classification of Diseases (9th Revision). The codes for lung cancer are 162.0-162.9 and for breast cancer are 174.0-174.9.

Age standardized mortality rates (ASMRs) are a summary of age adjusted death rates by gender that are standardized to a specific population to compare different time periods or geographical locations. The Vital Statistics data that are used in this report are standardized to 1971 Canada Census female population.

Standardized mortality ratios (SMRs) are the ratio of the actual number of deaths in a Local Health Area (LHA) to the expected number of deaths in that area that are based on provincial age-specific mortality rates (SMRs are used for comparing each LHA’s observed lung and breast cancer mortality to that of the Province as a whole).

The age standardized incidence rates were obtained from the B.C. Cancer Agency annual reports. The incidence rates are based on the number of new cases of cancer per 10,000 for a fixed population in each gender and age category. This rate eliminates the effect of the changing age structure of the population as a factor in determining risk of developing cancer; therefore, it is an appropriate measure to use when examining changes in risk over time. 1971 Canada census female population was used as the standard for this data.

Data for provincial and national comparisons was obtained from Statistics Canada reports. The ASMR measures that were used in these reports were standardized to 1991 Canada female population.

It should be noted that age standardized rates represented in this report are derived from 1971 (BC Vital Statistics Agency and BC Cancer Agency) and 1991 (Statistics Canada) Canada census population. Rates based upon different standards should not be compared.

 

II. Lung Cancer

As noted before, lung cancer is the number one cause of cancer deaths among women in British Columbia. In 1996, 24 percent of all female cancer deaths was caused by lung cancer. Overall, lung cancer is the third leading cause of death for women in British Columbia.

Table 1
Female Deaths Due to Lung Cancer by Age Group
British Columbia, 1987 to 1996

• In 1996, 810 females died of lung cancer.
• From 1987 to 1996, a total of 6,660 females lost their lives to lung cancer. The highest number of deaths were for those aged 65 to 79 for each year in that period.

Figure 4
Age Specific Death Rates for Female Lung Cancer
British Columbia, 1987 - 1996

Note: Rate per 10,000 female population in the specified age group.

 

• The highest rate of female lung cancer deaths was in individuals who were between 80-84 (24.21).
• Up to age 84, the rate of lung cancer mortality increased with age, but the rate declined for women 85 years of age and older.
• The sharpest increase in risk of dying from lung cancer occurred at age 65-69. Women age 65 and over were almost three times more likely to die of lung cancer than were women age 45 to 64.

Figure 5
Age Standardized Incidence Rates for Female Lung Cancer
British Columbia, 1974 to 1994

Note: Rate per 10,000 female standard (1971 Canada Census) population.
Source: BC Cancer Agency Annual Reports, 1974-1995.

 

• In the twenty years from 1974 to 1994 the general trend in incidence of lung cancer in women tended to increase.
• A higher rate of females were diagnosed with lung cancer for the majority of years in the 1990s as opposed to the 1980s and 1970s.
• Since lung cancer is usually not detected until advanced stages, an increase in incidence rates could equate to an increase in mortality rates.

Figure 6
Age Standardized Incidence and Mortality Rates
for Female Lung Cancer
British Columbia, 1984 to 1994

Note: Shaded area represents differences between incidence and mortality. Rate per 10,000
female standard population (using 1971 Canada Census as standard)
Source: BC Cancer Agency Annual Reports, 1974-1995.

 

• For the most part, age standardized mortality and incidence rates for lung cancer had the same patterns for the years 1984 -1994 with the exception of 1984 to 1985 and 1991 to 1992. From the mid 1980s to 1990, both the mortality and incidence rates increased steadily. Both mortality and incidence rates had the highest levels in 1993.
• Since the symptoms of lung cancer do not often appear until the disease is in its advanced stages, the gap between the incidence and mortality rates tends to be smaller than other types of cancers where early detection leads to increased incidence and relatively better survival (see breast cancer (Figure 10) as an example).

Table 2
Standardized Mortality Ratios for Female Lung Cancer by Local Health Area
British Columbia, 1987 - 1996

Note: SMR - standardized mortality ratio (Observed/Expected). Cells that are bolded (black background) indicate a statistically significantly high difference between the observed and expected deaths and cells that are italicized (gray background) indicate a statistically significantly low difference between the observed and expected deaths(p<0.05, two tailed). + significance based on less than 5 deaths.

• Based on SMRs, six Local Health Areas (LHAs) showed statistically significantly more female deaths from lung cancer than were expected. These were: Sooke (1.51), Cowichan (1.39), Prince George (1.35), Langley (1.25), Kamloops (1.22), and Coquitlam (1.17).
• The areas that showed statistically significantly fewer deaths than were expected (based on 5 or more deaths) were: Smithers (0.42), Vernon (0.76), Saanich (0.78), Abbotsford (0.79), West Vancouver-Bowen Island (0.80) Penticton (0.80), Central Okanagan (0.81) and Vancouver (0.92).

 

National and Provincial Comparisons

Figure 7
Age Standardized Mortality Rates
for Lung Cancer for Women
Canada and Provinces, 1994

Note: Rate per 10,000 female standard population (ASMRs derived using 1991 Canada Census female population).
Source:Canadian Cancer Statistics, National Cancer Institute, Statistics Canada, 1996

 

• In 1994, the age standardized mortality rate for lung cancer for females in Canada was 3.17 per 10,000 female standard population.
• Six of the ten provinces surpassed the national level of mortality with the highest being P.E.I. at a rate of 5.16. The second highest rate was in Manitoba at 3.57 with B.C. closely behind at 3.40.
• At a rate of 2.15, Newfoundland had the lowest rate of female lung cancer mortality in the nation.

 

Smoking and Lung Cancer

A section on the Medical Certification of Death requesting confirmation of certain “lifestyle” conditions (including tobacco use) was initiated by Vital Statistics Agency in 1994; however, it is probable that this information is underreported. Vital Statistics death records indicated that in 1996, of the total number of female lung cancer deaths, at least 50 percent were confirmed smokers. Based on 5 year age groups, the proportion of females who died of lung cancer and were smokers was 50 percent or over for all age groups except 35-39(44%), 65-69(46%), 75-79(46%), 80-84 (48%) and 85 and over (22%). There are plans to compare these deaths of confirmed smokers with the estimating measure now in use (SAMs) using 1995 and 1996 data.

In 1996, of 810 female lung cancer deaths, 644 were attributed to smoking. This was based on a fixed smoking-attributable mortality (SAM) of 79.6 percent and is derived by applying the SAM% to the number of deaths after certain ages in specific categories of diseases, in this case lung cancer.

Over the years, a number of studies have examined the relationship between lung cancer and smoking. The following studies and their results are worth mentioning:

• In a 1994 cohort study, Villeneuve and Mao examined the lifetime risks of developing lung cancer for six hypothetical cohorts (males, females, male current smokers, male never smokers, female current smokers and female never smokers). They found that 172 of the 1,000 male current smokers will eventually develop lung cancer and 116 of the 1,000 female current smokers are also likely to develop lung cancer. The never smokers showed a remarkable decrease in their chances of developing lung cancer (96/1,000 and 43/1,000 for males and females respectively).¹⁶
• Under the guidance of American Cancer Society’s Advisory Committee on Statistics, Drs. Hammand and Horn performed an investigation scheme in which the smoking histories of a very large number of men not known to have cancer of the lung were recorded. The histories of over 187,000 men between the ages of 50 and 70 were recorded which included men who had never smoked and those who were regular smokers. The results were that the death rate among the regular smokers was one and a half times greater than the rate among non-smokers. The cancer death rate was two and a half times greater in heavy smokers (one pack or more a day) than in non-smokers. The death rate from cancer of the lung was at least five times higher in the heavy cigarette smoking group than in non-smokers.⁶
• The U.S. Cancer Research Institute reported that smoking is responsible for about 85 percent of lung cancer deaths. “Cigarette smoke contains more than 4,000 different chemicals, many of which are proven carcinogens, while hundreds of others increase the cancer-causing power of carcinogens.⁶
• The Prevention Care Program of the B.C. Ministry of Health and Ministry Responsible for Seniors recently attributed at least eight types of cancers as well as hypertension and heart disease to smoking.
• The American Lung Association recently reported that female smokers aged 35 or older are 12 times more likely to die prematurely from lung cancer than female non-smokers.²
• In 1996, the Canadian Cancer Society reported that more than 85 percent of lung cancers are caused by smoking. Once diagnosed with lung cancer, over 80 percent of the individuals die within five years of diagnoses.³

 

III. Breast Cancer

Breast cancer is the second highest cause of cancer death among women in British Columbia. In 1996, 590 women died of breast cancer representing 18 percent of all female cancer deaths. Breast cancer is also the most frequently diagnosed form of cancer, for the most part due to the wide spread use of screening mammography. Although some studies have shown that several risk factors are associated with breast cancer – such as late menopause, no children or first child after age of 35 and family history of breast cancer – more than 70 percent of women who are diagnosed with breast cancer do not have any of the risk factors present.⁷

 

• A total of 5,292 women died of breast cancer between 1987 and 1996.
• The highest number of deaths from breast cancer were for those aged between 65 and 69 in the same period.

Table 3
Female Deaths Due to Breast Cancer by Age Group
British Columbia, 1987 to 1996

Figure 8
Age Specific Death Rates for Female Breast Cancer
British Columbia, 1987-1995

Note: Rate per 10,000 female population in the specified age group.

 

• The risk of dying from breast cancer increased with age for women in British Columbia.
• The lowest age specific death rate for breast cancer was found in the age group of 25-29 while the highest level was detected among those aged 85 and over.

Figure 9
Age Standardized Incidence Rates for Female Breast Cancer
British Columbia, 1974 to 1994

Note: Rate per 10,000 female standard population (derived using 1971 Canada census population as a standard).
Source: BC Cancer Agency Annual Reports, 1974-1995.

 

• There has been an overall increase in age standardized incidence rates for breast cancer for females from 1974 to 1994.
• The incidence rates peaked to the highest level in 1988. This increase may have been related to hightened awareness of mammography fueled by the start of the British Columbia Mammography Screening Program. It is probable that more women had mammograms and thus, were diagnosed in 1988 than in previous years.

Figure 10
Age Standardized Incidence and Mortality Rates
for Female Breast Cancer
British Columbia, 1984 to 1994

Note: Shaded area represents the difference between incidence and mortality.
Rate per 10,000 female standard population (derived using 1971 Canada census population as a standard).
Source: BC Cancer Agency Annual Reports, 1974-1995.

 

• As illustrated in Figure 10, there was a large gap between incidence and mortality rates from 1984 to 1994 in British Columbia indicating a relatively better survival rate from breast cancer when compared to lung cancer (see Figure 6).
• The increasing use of mammography in the late 1980s contributed to a sharp increase in the incidence rates for breast cancer. Although the incidence rates declined in the early 1990s, the levels were still higher than the early 1980s.
• There has been a slight reduction in the mortality rates for breast cancer from 1984 to 1994.

Table 4
Standardized Mortality Ratios for Female Breast Cancer by Local Health Area
British Columbia, 1987-1996

Note: SMR - standardized mortality ratio (Observed/Expected). Cells that are bolded (black background) indicate a statistically significantly high difference between the observed and expected deaths and cells that are italicized (gray background) indicate a statistically significantly low difference between the observed and expected deaths(p<0.05, two tailed). + significance based on less than 5 deaths.

 

• Based on SMRs, three Local Health Areas (LHAs) showed statistically significantly more deaths from breast cancer than were expected. These were Fernie (1.63), Vernon (1.26) and Greater Victoria (1.14).
• The two areas that showed statistically significantly fewer deaths (based on 5 or more deaths) than were expected were: Cariboo-Chilcotin (0.66), and Vancouver (0.92).

Figure 11
Age Standardized Mortality Rates for Female Breast Cancer
Canada and Provinces, 1994

Note: Rate per 10,000 female standard population (ASMRs derived using 1991 Canada Census as standard population).
Source: Canadian Cancer Statistics, National Cancer Institute, Statistics Canada, 1996.

 

• The age standardized mortality rate (ASMR) for female breast cancer in Canada was 2.98 in 1994.
• Among all provinces, B.C. had the lowest ASMR at 2.63. Alberta tied the national level at 2.98 and both Quebec and Ontario had levels above the national level at 3.17 and 3.05 respectively.

The Mammography Program in Canada and British Columbia

Mammography was originally developed in the early part of the century but was not widely used until the 1950s. For the most part, mammography was used as a diagnostic tool for women with symptoms of breast pathology. Since the 1980s, mammograms have been used for screening healthy women in particular age groups for early detection purposes as well as women with signs of breast cancer. “From 1981 to 1994, the annual number of mammograms performed in Canada increased from less than 200,000 to more than 1.4 million”.⁸

Mammography Data and its Limitation

The data used for Figures 12 and 13 were obtained from Statistics Canada Health Report Vol. 8(3). The data for the breast screening program used in the report are provided by provincial breast screening programs and health departments as well as the 1994-95 National Population Health Survey. The survey had a sample size of 27,263 household residents in all provinces except people living on Indian Reserves, on Canadian Force bases or remote areas. In the survey women were asked “have you ever had a mammogram?” If answered yes, they were further asked “When was the last time?” The final data analyzed in the Statistics Canada report were based on 5,030 responses from women aged 40 years and over who participated in the survey.

It should be noted that the total mammography rates for women 40 years and over may be overestimated. Some women may have had more than one mammogram in a given year. The overestimation was calculated to be around 10 percent by the authors of the report. In addition, there were also some differences between the data from the administrative sources (provincial screening programs and health departments) and the National Population Health Survey due to underreporting and mammograms received from other sources other than breast screening programs which appeared on the survey but not the screening program.

The graphical representations regarding mammography in Figures 12 and 13 should be considered with these limitations in mind and may vary from other published sources.

Figure 12
Percentage Mammograms Conducted by Breast Screening and Health Programs
for Females 40 Years of Age and Over
British Columbia, 1988 to 1994

Note: Percent of female population in specified age group.
Source:Trends in Mamography Utilization, 1981-1994, Health Reports, Statistics Canada, Vol. 8(3), Winter 1996.

 

• There was a significant increase in the proportion of women who had screening mammography from 1988 to 1994. In 1988, only 5% of women aged 40 to 49 had screening mammography while in 1994 this proportion increased to 50%. The increase in the proportion of screening mammography was also significant for those in the 50 to 59 and 60 to 69 age groups (5% to 51% and 4% to 53% respectively).

Figure 13
Percentage of Women 40 Years and Over
Who Have Ever Had a Mammogram
Canada and Provinces, 1994 - 1995
(from 94/95 National Population Health Survey)

Source:Trends in Mamography Utilization, 1981-1994, Health Reports, Statistics Canada, Vol. 8(3), Winter 1996.

 

• Based on the provincial screening programs and the National Population Health Survey performed between 1994 and 1995, 64% of all Canadian women over the age of 40 had ever had a screening mammogram.
• British Columbia had the highest rate of mammograms at 69%. Quebec had the second highest rate at 67%, followed by Alberta and Saskatchewan at 65%. The province with the lowest percentage of mammograms was Newfoundland.

There have been many initiatives in Canada that have all contributed to early detection of breast cancer and reducing breast cancer mortality. Some of the breast screening initiatives were identified by Gaudette, L. et al. in a recent study in 1996. These initiatives were:

 

The National Breast Screening Study

Based on a cohort group identified in the national breast screening survey that took place in the early 1970s, the first study on mammography in Canada was initiated. The study was designed to evaluate the effect of mammography screening on incidence and mortality rates among women aged 40-59. As a follow-up, from January 1980 through March 1985, 50,430 women aged 40-49 and 39,405 women aged 50-59 were involved in the study.

The results which were published in 1992 indicated that during the 7 year follow up, mammography and physical examination had not had a significant impact on breast cancer mortality. An 11 year follow-up on incidence and a 13 year follow-up on mortality will be published in the near future.⁸

 

Workshop on the Early Detection of Breast Cancer

This workshop took place in 1988. The report of the workshop which was developed by government representatives, volunteer and professional groups from all over Canada recommended that women aged 50-69 be offered and encouraged to participate in a screening mammography program. The workshop proposed the establishment of screening centres to ensure the highest standards in image quality, interpretation and follow-up with the lowest possible costs.⁸

 

Provincial Screening Programs

British Columbia was the first province to set up a breast screening program in 1988. Other provinces such as Saskatchewan, Ontario and Alberta started their screening programs in 1990 and Nova Scotia and Yukon followed shortly in 1991. Manitoba and New Brunswick started their programs in 1995 and Newfoundland started in 1996. Up to 1996, the only province that did not have a provincial screening program was Quebec.

At first, British Columbia provided annual screening for women aged 40 and over, but since 1995 has concentrated on those aged 50-70. “The goal of the provincial programs is to screen 70 percent of their target population and achieve a 30 percent reduction in mortality.⁸

 

The National Forum on Breast Cancer

The National Forum on breast cancer took place in Montreal in November 1993 under the sponsorship of the Canadian Cancer Society, the National Cancer Institute of Canada, the Medical Research Council, the Canadian Breast Cancer Foundation and Health Canada. The Forum recommended an increase in funding to allow provincial programs to reach the majority of women aged 50-69 for screening mammography every two years.⁸

 

British Columbia Government Initiative

On October 8th, 1996, B.C. Health Minister Joy MacPhail announced a plan to contribute more resources to a number of provincial programs in support of initiatives to reduce breast cancer mortality. Some of these initiatives were:

 

• To set aside the amount of $6.8 million for the Screening Mammography Program of B.C. Today, the program has 24 centres throughout British Columbia including four mobile clinics for rural and isolated areas;
• To develop a pilot program between the BC Cancer Agency and BC’s Women’s Hospital to reduce the time for a definitive diagnosis of women who have abnormal screenings mammogram results as well as providing counselling and education;
• To develop a preventive care advertising campaign to encourage women to access screening mammography services in their communities;
• To spend an amount of $25,000 to work with the Breast Cancer Information Project to sponsor breast cancer forums, enabling communities to raise awareness about breast cancer and increase support for women living with breast cancer.
• Has designated (1994) an amount of $750,000 over five years to the Centre for Breast Cancer Prevention for the purposes of treatment and research on evaluation of the outcome of treatment programs;
• To produce a video documentary on the subject of First Nations Women and Breast Cancer.

 

The Impact of Mammography on Breast Cancer Incidence and Mortality

The screening mammography procedure has been used substantially since the 1980s in Canada. With the increase in screening, there has been an increase in the incidence rates of breast cancer among women. This does not necessarily mean that the number of women with breast cancer is on the rise but rather that more women are being diagnosed at the early stages of the disease than ever before.

The direct impact of mammograms on breast cancer mortality is still unknown. Although, research has shown that in both United States and Canada, breast cancer mortality has been at the lowest levels since the 1950s, it is still early to make a conclusion.⁸ In addition, a fall in breast cancer mortality has also been reported in United Kingdom particularly among women 55-69 years of age.¹¹ However, researchers believe that screening mammography and early detection is only partly responsible for this decline and improved treatment and medical intervention such as tamoxifen therapy has also played a significant part in the reduction of breast cancer mortality.

At this time, it is difficult to statistically demonstrate the direct impact of mammography on breast cancer mortality among women of various ages. Continuing research and monitoring is needed to determine whether mammography and early detection leads to a significant reduction in breast cancer mortality.

 

References

1. American Cancer Society, Study Links Smoking and Increased Risk of Fatal Breast Cancer, American Cancer Society, May 1994

2. American Lung Association. American Lung Association Fact Sheet - Women and Smoking, American Lung Association, 1996

3. Canadian Cancer Society, Facts on Smoking, 1996

4. Bryant, Heather, et al., Risks and Probabilities of Breast Cancer: Short-term versus lifetime probabilities, Canadian Medical Association Journal, 150(2), 1994

5. BC Cancer Agency. Annual Reports, 1974-1995

6. Cameron, Charles S., Lung Cancer and Smoking: What we really know, 1956

7. Dawson, Deborah A., Breast Cancer Risk Factors and Screening, Division of Vital Statistics, National Center for Health Statistics, United States, 1987

8. Gaudette, Leslie et al., Trends in Mammography Utilization, 1981 to 1994, Health Reports, Statistics Canada, Vol. 8(3), Winter 1996

9. Gaudette, Leslie et al., Update on breast cancer mortality, 1995, Health Reports, Statistics Canada, Vol. 9(1), Summer 1997

10. Kelsey, J. et al., The Epidemiology of Breast Cancer, Cancer Journal for Clinicians Vol. 41, 1991

11. National Cancer Institute., NCI Reports improvements in Breast Cancer Death Rate, 1996.

12. National Research Institute, Canadian Cancer Statistics, 1996

13. Probert, Adam, et al., Recent Trends in Lung Cancer Among Canadians Ages 25-44, Canadian Journal of Public Health, Vol. 83(6), 1992

14. Screening Mammography Program of British Columbia, 1995/96 Annual Report

15. Stanford Medical Center, Smoking and Lung Cancer: An Undeniable Connection, Fall 1994

16. Villeneuve, P.J. & Yang Mao. Lifetime Probability of Developing Lung Cancer by Smoking Status, Canada, Canadian Journal of Public Health, Vol. 85(6) 1994

17. Vital Statistics Agency, Selected Vital Statistics and Health Status Indicators, British Columbia, 125th Annual Report, 1996

Glossary

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Age Standardized Mortality Rate (ASMR): A summary of age adjusted death rates by gender which have been standardized to a specific population for the purpose of rate comparisons of different time periods or different geographical locations. In this report, ASMRs for females were standardized using Canada Census female population. Rates prepared by the British Columbia Vital Statistics Agency and those obtained from BC Cancer Agency reports were derived using 1971 Canada Census as a standard. Provincial/national ASMR comparisons from Statistics Canada publications utilized 1991 Canada Census population.

Alcohol-Related:
This category includes all deaths stated as being directly or indirectly related to alcohol. It should be noted that where alcohol is an indirect cause of death (i.e. not primary) and the direct underlying cause of death falls within one of our selected causes (e.g. motor vehicle accidents), then this death may be counted in both columns. That is, not all of "alcohol related" are exclusive. This category includes ICD-9 codes - 291, 303, 305.0, 357.5, 425.5, 535.3, 571.0-571.3, 571.5, 577.1, 648.4, 760.7, E860, 790.3.

Assignment of Health Region:
Cases are assigned to Health Regions by the aggregation of appropriate LHAs.

Assignment of Local Health Area (LHA):
Allocation of LHA, in the case of births and deaths is based upon the usual residence (by postal code) of the mother and deceased respectively. Marriages are assigned to LHAs according to the place of event. Standard Geographical Code (SGC), derived from community name, is used in the absence of postal code.

Elderly Gravida:
Any mother who was 35 years of age or older at the time of delivery of a live born infant.

External Causes of Death:
Deaths due to environmental events, circumstances and conditions as the cause of injury, poisoning, and other adverse effects. Broad categories include accidents, suicide, medical or abnormal reactions, homicide, legal intervention, misadventures and injury from war operations. Standard tables under this heading include deaths due to accidents, suicide, homicide and other. Accidents are subdivided by the following categories; motor vehicle accidents (MVA) (ICD E810-E825, E929.0), poisoning (E850-869, E929.2), falls (E880-E888, E929.3), burns/fire (E890-899, E924, E929.4), drowning (E830, E832, E910), other accidents - all codes from E800-E949 not already noted. Suicide ICD-9 codes are E950-E959; homicide (E960-969); "other" consists of legal intervention (E970-978), undetermined if accidental or purposely inflicted (E980-989) and war operations (E990-999).

Heart Disease:
Tables under this heading include deaths due to:

• rheumatic/valvular: 391-398, 424
• hypertension: 401-405
• ischemic: 410-414, 429.2
• conductive & dysrythmic: 426-427
• heart failure: 428
• congenital: 745-746
• other: pulmonary - 415-417, inflammatory - 420-423, 429.0, cardiomyopathy - 425, 429.3, degenerative - 429.1, other, ill-defined or unspecified - 429.4-429.9

ICD-9:
The ninth revision of International Classification of Diseases, World Health Organization, Geneva, 1977. An internationally used system of approximately 12,000 four digit numbers representing a system of categories to which morbid entities are assigned according to an established criteria. ICD provides a common basis of disease and injury classification that facilitates storage, retrieval, and tabulation of statistical data.

Infant Deaths:
Deaths of children under one year of age.

Low Birth Weight:
Any liveborn infant weighing less than 2500 grams.

Neoplasms (ICD-9 140-239):
Although the vast majority of deaths in this category are due to malignant cancer, also included are benign, in-situ, and unspecified "tumours". Detailed ICD-9 breakdown used in "Neoplasm Deaths" tables are;

• lung: includes trachea, bronchus, lung (ICD-162) and pleura (163)
• female breast: (ICD-174)
• colorectal: includes colon (ICD-153) and rectum, rectosigmoid junction and anus (154) other G.I. (Gastrointestinal): includes esophagus (ICD-150), stomach (151), small intestine and duodenum (152), liver & intrahepatic bile ducts (155), gallbladder and extra-hepatic ducts (156), pancreas (157), peritoneum (158), other and ill-defined within digestive organs (159).
• female reproductive: includes uterus (ICD-179), cervix (180, 182), placenta (181), ovary and adnexa (183), vagina & external genitalia (184).
• male reproductive: includes prostate (ICD-185), testis (186), penis & other genitalia (187).
• blood lymph: includes lymphatic and haematopoietic tissue (200-208).
• other malignancy: includes malignant neoplasms of other (e.g. lip, oral cavity, pharynx, nose, ear, larynx, heart, bone and connective tissue, urinary tract, eye, brain, endocrine glands), ill-defined or unspecified sites (140- 149, 160, 161, 164, 165, 170-173, 175, 188-189, 190-199).
• non-malignant & unspecified: includes benign (210-229), in-situ (230-234), and neoplasms of unspecified nature (e.g. "tumor" - 239).

Other Selected Death Statistics:
Tables under this heading inlcude deaths due to:

• respiratory disease with four sub-categories of emphysema (ICD-492), chronic obstructive pulmonary disease (COPD) (496), pneumonia/influenza (480-487), and other respiratory diseases (ICD-460-478, 490-491, 493-495, 500-519).
• diabetes (250)
• alcohol related - see above.
• AIDS: includes AIDS and HIV infections (ICD-042-044).
• cerebro and other vascular: includes cerebrovascular disease (ICD-430-438), disease of arteries and veins (440-456), hypotension (458), and other circulatory system disease (459).
• liver disease: ICD-570-573.

Premature / Pre-term:
Any live born infant less than 37 weeks gestation at delivery.

Smoking-Attributable Mortality (SAM):
SAM is an estimation technique used to approximate the extent of smoking-attributable deaths. Estimation methods, while not precise, may at least provide a general indication of the extent of such deaths. The method used here is based on the concept of attributable risk.

To define attributable risk mathematically, consider d₀ and d₁ respectively to represent the death rates, in a given time period, in two cohorts from a population - those not exposed and those exposed to a given risk factor. The attributable risk of this factor, AR₁ , would then be:

Where:

r₁ = d₁/d₀ is the relative risk of the exposed cohort.
The relative risk of the unexposed cohort is r₀ = 1; the attributable risk of this cohort is AR₀ = 0.
The attributable risk (AR) for the population as a whole (exposed plus unexposed cohorts) is given by:

Where:

p₁ = the proportion or fraction of the population exposed to the risk factor; and
1-p₁ = the proportion or fraction of the population not exposed to the risk factor.

This may be extended to account for multiple levels of exposure as follows:

Where:

p_i = the proportion (prevalence) of the population in the ith level of exposure group;
r_i = the relative risk at the ith level of exposure; and
i = the ith risk category.

When applied to smoking-attributable mortality (SAM), the attributable risk is often expressed as a percentage:

SAM (%) = AR x 100

The number of adult (35+ years of age) smoking deaths in British Columbia were estimated for 19 diseases. Smoking-attributable deaths are derived by multiplying the smoking-attributable mortality percentage expressed as a decimal fraction by the number of deaths in each diagnostic category listed below.

Relative-risk data from the American Cancer Society's Cancer Prevention Study (CPS) II (1982-1988) (Centers for Disease Control, 1991) were selected for use, as they have been widely used for similar analyses. The data from the CPS-II established the age groups and the classification of smokers (current, former, and never) for which prevalence data were required. The prevalence data used in this analysis are from a 1989 Statistics Canada survey (Stephens, 1991). The data by age group categories include the age group 25-44, whereas the relative-risk data is for the age categories 35+, or 35-64 and 65+. It has been assumed that the prevalence rate was equal for those aged 25-34 and those 35-44. The 1989 prevalence data were not provided by provincial age group breakdowns. The 1989 provincial-prevalence age group rates were approximated by adjusting the 1989 Canadian rates for males and females. To do this, the national rates were multiplied by the ratio of overall provincial to national prevalence rates, separately for current and former smokers. SAM can be considered as a health status indicator.

Standardized Mortality Ratio (SMR):
The ratio of the number of deaths occurring to residents of a geographic area (e.g. LHA) to the expected number of deaths in that area based on provincial age specific mortality rates.

Stillbirth:
The complete expulsion or extraction from its mother after at least 20 weeks of pregnancy or after attaining a weight of at least 500 grams, of a product of conception in which, after expulsion or extraction, there is no breathing, beating of the heart, pulsation of the umbilical cord or unmistakable movement of voluntary muscle.

Teenage Mother:
Any mother who was age 19 or less at the time of delivery.

UCOD:
Underlying cause of death - based upon application of standard international coding rules for determining consequential relationships of conditions and diseases from immediate cause backwards to underlying cause.

Contributors' Note:

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The editorial staff would like to invite any readers who wish to contribute an article or paper summary for publication in this Quarterly Digest to contact the Information and Resource Management Branch of the British Columbia Vital Statistics Agency. Articles should focus on health status issues in British Columbia. It is preferable that submissions be in "electronic media" format (e.g. Word, Word Perfect, Excel, Lotus 123, Power Point, Corel Draw, etc.). Article presentation will be subject to space allowances and publishing deadlines.

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