Breast Cancer in Ontario 1971-1996 Preface/Highlights/Background
Anna M Chiarelli Beth Theis Eric Holowaty Veronika Moravan E Diane Nishri October 2000
Surveillance Unit and The Ontario Breast Screening Program Division of Preventive Oncology Cancer Care Ontario
Breast Cancer in Ontario
Table of Contents Preface ............................................................................................................................................. ii Report Highlights .............................................................................................................................. iii Background ....................................................................................................................................... 1 Introduction .......................................................................................................................... 2 Anatomy ............................................................................................................................... 3 Pathology of invasive carcinoma of the breast ....................................................................... 3 Risk factors .......................................................................................................................... 4 Prevention and early detection .............................................................................................. 5 Signs and symptoms .............................................................................................................. 7 Diagnosis and staging ............................................................................................................ 7 Treatment ............................................................................................................................. 8 Prognosis .............................................................................................................................. 9
List of Tables Table 1.
Probability of developing breast cancer by age, and lifetime ............................................ 2 probability of dying from breast cancer, in Canada (NCIC 2000)
Table 2.
Proportion of Ontario women aged 50-69 having a screening .......................................... 6 mammogram within the last two years, reported by the NPHS and within the OBSP, by region, 1996-1997
Table 3.
Comparison of stage distribution in OCR versus SEER ................................................... 8
List of Figures Figure 1.
Anatomy of the female breast ......................................................................................... 3
Figure 2.
Proportion of Canadian women aged 50-69 reporting a screening .................................... 7 mammogram within the last two years, National Population Health Survey (NPHS), 1996-1997
Figure 3.
Five-year relative survival, by stage, for US SEER breast cancer cases, ......................... 9 1990-1991
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Breast Cancer in Ontario
Preface This monograph presents information on incidence, mortality and survival for invasive breast cancer in Ontario females from 1971 to 1996. It was developed to provide comprehensive background information for the Ontario Breast Screening Program (OBSP) and as a resource document for planning. The basis for the information in this monograph is the Ontario Cancer Registry (OCR). Both the OBSP and the OCR are operated by Cancer Care Ontario (CCO), through funding by the Ontario Ministry of Health and Long-Term Care. The OBSP and the OCR are situated within the Screening Unit and the Surveillance Unit, respectively, of the Division of Preventive Oncology, which is located at the Provincial Office of CCO in Toronto. The authors would like to thank Drs. Frances O’Malley and Carol Sawka for contributing to the clinical sections in the background and to Mr. Gordon Fehringer for providing projected numbers for breast cancer cases and deaths. We are also grateful to Dr. Richard Schabas, Head of the Division of Preventive Oncology and Dr. Verna Mai, Director of the Screening Unit, for reviewing a draft of this document. This monograph could not have been produced without the valuable assistance of Mrs. Virginia Hunter (desktop publishing), and Ms. Vicky Majpruz-Moat and Ms. Sandrene Chin Cheong (technical support and graphics). Finally, the authors would like to acknowledge the contribution of all the operations staff within the Surveillance Unit, and the Registry Support Group (within the Information Systems Department), for their ongoing efforts in ensuring the generation of timely and high-quality cancer incidence data for Ontario.
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Breast Cancer in Ontario
Report Highlights •
In the year 2000, breast cancer will be diagnosed in an estimated 7,200 Ontario women and an estimated 2,000 women will die from the disease.
•
In 1992-1996, breast cancer was the most common cancer site among women, representing 29% of the total cancers, and ranked first for every age group. Breast cancer was also the most common cause of death during this time period, accounting for 19% of all cancer deaths.
•
Breast cancer incidence varies dramatically around the world. Ontario’s incidence rate is among the highest in the world.
•
The incidence of breast cancer in Ontario has increased by 17% from 1971 to 1996. This increase was highest for women over 50 years of age, particularly after 1986.
•
Mortality rates increased slightly (4%) from 1971 to 1986. Between 1986 and 1996, breast cancer mortality decreased by 9%. This decline was greatest for women aged 40-49 and 50-69. The decline is most likely due both to screening and improved treatments.
•
The five-year relative survival rate after diagnosis of breast cancer is 81%. The greatest improvements in survival occurred during the 1980s. Relative survival was highest for women diagnosed at ages 40-69 and lowest for women diagnosed at ages 20-39.
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Breast Cancer in Ontario
Background
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Breast Cancer in Ontario
Introduction About 7,200 Ontario women will be diagnosed with breast cancer in 2000 and an estimated 2,000 women will die from it. Breast cancer is the most common cancer in Ontario women. Although lung cancer causes more deaths overall, breast cancer is the most common fatal cancer in women under age 50. Incidence and mortality are higher, however, for older age groups; the probability of developing breast cancer increases steeply as a woman ages (Table 1). The overall incidence rate increased by 17% between 1971 and 1996. In contrast, the mortality rate increased slightly (4%) from 1971 to 1986 and has been declining since this time. Table 1. Probability1 of developing breast cancer by age, and lifetime probability of dying from breast cancer, in Canada (NCIC 2000) Cumulative probability1 (%) of developing breast cancer by age:
Lifetime probability of dying
Age Probability
% 3.9
1
40 0.4
50 1.7
60 4.0
70 6.9
80 10.1
90 12.3
One in: 25.8
The probability of developing cancer is calculated based on age- and sex-specific cancer incidence and mortality rates for Canada in 1995 and on life tables based on 1994-1996 all-cause mortality rates. The probability of dying from cancer represents the proportion of persons dying from cancer in a cohort subjected to the mortality conditions prevailing in the population at large in 1997.
This report only examines invasive breast cancer in women. Men also get breast cancer. Male breast cancer is not included in this report because there are only about 40 cases diagnosed in Ontario in any year. Such small numbers make it difficult to make meaningful observations about time trends and geographic patterns.
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Breast Cancer in Ontario Anatomy The female breast consists of three major components: glandular tissue, subcutaneous tissue and skin. The glandular tissue consists of breast parenchyma and stroma. The tip of the nipple contains openings of collecting ducts through which the infant obtains milk. The ducts extend from the nipple to form a branching duct system that divides the breast into approximately 20 lobes (Figure 1). Each duct drains a lobe and each lobe comprises 20-40 lobules. Lobules are formed by multiple blind ending branches of the terminal ducts. Figure 1.
Anatomy of the female breast
Rib Muscle
Lobes
Ducts
Nipple Areola Fat
Source: National Cancer Institute
Pathology of invasive carcinoma of the breast Invasive carcinoma of the breast is usually divided into tumours of no special morphologic type (infiltrating duct) and those of a special type. Infiltrating duct carcinoma comprises approximately 70% of breast cancers (Berg and Hutter 1995). These tumours can be stratified into prognostic groups based on histologic grading. Other types of carcinoma comprise approximately 30% of all invasive breast cancers (Page et al. 1987). These include lobular, mucinous, tubular, cribriform and medullary cancers. Tubular and cribriform cancers are generally associated with a more favourable prognosis than the other types.
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Breast Cancer in Ontario Risk factors Age is the most significant risk factor for breast cancer. The risk of a woman developing breast cancer increases rapidly with age (Bryant and Brasher 1994). Being born in North America or Northern Europe is also an important risk factor for breast cancer. Risk is slightly higher for women living in urban areas and belonging to a higher socioeconomic class (Kelsey and Bernstein 1996). Some reproductive characteristics influence the risk of breast cancer. Early age at menarche, late age at menopause, late age at first full-term pregnancy and never having had children are all associated with modest elevations in risk (Kelsey et al. 1993). Removal of ovaries before age 40 reduces the risk by about one-half. Women currently using oral contraceptives (OC) are at a slightly increased risk of developing breast cancer, but there is no increased risk 10 years after stopping OC use (Collaborative Group on Hormonal Factors in Breast Cancer 1996). Hormone replacement therapy slightly increases risk and this risk increases with length of use (Collaborative Group on Hormonal Factors in Breast Cancer 1997). This excess risk decreases after hormone replacement therapy is stopped and has largely disappeared after five years. Recent data show that replacement therapy with both estrogen and progestin increases breast cancer risk beyond that associated with replacement with estrogen alone (Schairer et al. 2000). A family history of breast cancer is an important risk factor (Pharoah et al. 1997). This risk is particularly high if both the mother and a sister have been affected at a younger age (less than 50). Mutations in several identified genes account for some of this familial clustering. Mutations in the BRCA1 and BCRA2 genes are associated with an inherited susceptibility to breast cancer at an early age and are estimated to account for between 3% and 8% of all breast cancers (Brody and Biesecker 1998). Many studies have suggested causal roles for diet and alcohol consumption in breast cancer; these remain unverified (Clavel-Chapelon et al. 1997; Longnecker 1994). Postmenopausal obesity increases the risk of breast cancer. Obesity before the menopause, however, is protective (Hunter and Willett 1993; Ursin et al. 1995). Regular physical exercise probably reduces the risk of breast cancer, in particular for premenopausal women who are lean and have been pregnant (Friedenreich et al. 1998). Moderate to high doses of ionizing radiation to the chest before age 40 increases breast cancer risk. Results from studies of other exogenous exposures are inconclusive. The most recent large studies have found no evidence of an increased breast cancer risk associated with exposure to environmental pollutants such as the pesticide DDE (chemically related to DDT) and PCBs (polychlorinated biphenyls) (Laden and Hunter 1998). A number of breast conditions are considered predisposing or predictive factors. Benign proliferative breast disease with atypical hyperplasia increases the risk of breast cancer three- to five-fold and relative risks of around 2 have been found for proliferative disease without atypia (Kelsey and Bernstein 1996). Women with ductal carcinoma in situ, lobular carcinoma in situ, or a history of cancer in one breast are at high risk. Women with high (>75%) mammographic density (the proportion of connective tissue and epithelial tissue as opposed to fat) have a risk three to four times that of women whose parenchyma is mostly fat (Oza and Boyd 1993).
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Breast Cancer in Ontario Prevention and early detection Most of the established risk factors for breast cancer are associated with only moderate elevations in risk. Only a few are readily modifiable by either environmental or behavioural changes. Despite this, some primary prevention trials are underway or planned. Two randomized trials being conducted in North America will assess whether a low-fat diet reduces the incidence of breast cancer (Self et al. 1988; Boyd et al. 1997). A small randomized trial in Los Angeles, California, is testing whether a hormonal contraceptive regimen designed to suppress ovarian function lowers breast cancer risk (Spicer et al. 1993). Tamoxifen is being considered for the prevention of breast cancer because of its demonstrated effect in decreasing the risk of breast cancer recurrence. Results of three randomized controlled trials have recently been published. Preliminary results of the National Surgical Adjuvant Breast and Bowel Project (P-1) in the United States and Canada showed that tamoxifen use lowers the risk of breast cancer by 45% among users compared to women with the same risk factors who did not take tamoxifen (Fisher et al. 1998). Neither the British nor Italian trials have found any benefit from tamoxifen (Powles et al. 1998; Veronesi et al. 1998). Screening with regular mammograms can reduce breast cancer mortality in women aged 50-74. Randomized controlled trials show a mortality reduction of 26% (95% confidence interval 17% to 34%) (Kerlikowske et al. 1995). An organized breast cancer screening program was introduced in Ontario in 1990. The Ontario Breast Screening Program (OBSP) offers biennial screening to all women in the province 50 years of age and older. The OBSP offers eligible women two-view mammography, clinical breast examination by a specially trained nurse examiner, instruction in breast self-examination and client recall. In 1996-97, 61.5% of women aged 50-69 reported having had a screening mammogram in the last two years (Table 2). Only 11.6% of all Ontario women in that age group were screened within the OBSP. OBSP coverage was higher for some regions in the north such as Manitoulin Island and Sudbury and Thunder Bay, Kenora and Rainy River. Expansion of the OBSP since 1998 has increased the proportion of women 50-69 having their screening mammograms within the OBSP to 15.8% during 1998-1999. In 2000, OBSP will reach an estimated 21% of eligible women.
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Breast Cancer in Ontario Table 2. Proportion of Ontario women aged 50-69 having a screening mammogram within the last two years, reported by the NPHS and within the OBSP, by region, 1996-1997 National Population Health Survey (NPHS) Region1
NPHS (%)
OBSP 2 (%)
Algoma, Cochrane
63.7
24.5
Brant, Haldimand-Norfolk Bruce, Grey, Perth, Huron Durham Elgin, Middlesex, Oxford Essex Halton Hamilton-Wentworth Lambton, Kent Lanark, Leeds & Grenville, Hastings, Prince Edward, Frontenac, Lennox & Addington Manitoulin Island, Sudbury District, Sudbury Regional Municipality Niagara Northumberland, Victoria, Haliburton, Peterborough Ottawa-Carleton Peel Prescott & Russell, Stormont-Dundas & Glengarry, Renfrew Simcoe Thunder Bay, Kenora, Rainy River Timiskaming, Muskoka, Parry Sound, Nipissing Toronto Waterloo Wellington, Dufferin York All Ontario
50.3 58.2 63.8 57.4 65.2 57.4 61.1 73.3 58.2
3.4 12.1 2.9 20.4 17.6 3.6 27.4 6.2 24.3
66.3 61.4 67.3 62.3 58.6 59.3 58.3 65.1 48.9 63.7 56.1 64.2 67.0 61.5
43.1 1.6 6.7 22.7 0.8 10.8 1.5 30.0 8.0 7.8 6.6 7.3 6.7 11.6
1 2
Regions are agglomerations of census divisions Number of women aged 50-69 at screening who participated in OBSP as a proportion of all women aged 50-69 in that region, using 1996 Ontario census data
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Breast Cancer in Ontario The percentage of women reporting having had a screening mammogram in the last two years varies among provinces (Figure 2). Ontario has the highest reported coverage. Figure 2. Proportion of Canadian women aged 50-69 reporting a screening mammogram within the last two years, National Population Health Survey (NPHS), 1996-1997 Newfoundland Prince Edward Island Nova Scotia New Brunswick Que bec Ontario Manitoba Saskatchewan Alberta British Columbia 0
10
20
30
40
50
60
70
Percent
Signs and symptoms More and more breast cancers are now being detected by screening, before the development of symptoms. Symptomatic breast cancer is usually first noticed by the patient as a painless mass. A small proportion of patients report breast pain as the first symptom. Other less common symptoms include thickening, swelling, skin irritation or distortion in shape. Nipple symptoms, including spontaneous discharge, erosion, inversion or tenderness, may also occur. Many of these symptoms are more commonly associated with non-malignant processes, including fibrocystic disease and intraductal papillomas (Ahearne et al. 1998). Malaise, bony pain and weight loss are unusual, but may indicate metastatic disease. Mammographic findings most predictive of malignancy include spiculated masses with associated architectural distortion, clustered micro-calcifications in a linear or branching array, and/or micro-calcifications within a mass (Ahearne et al. 1998). While breast cancer may also appear as a round “coin-like” lesion, this is much less common (Henderson 1995). Diagnosis and staging The diagnosis of breast cancer typically begins with physical examination, mammography and, sometimes, ultrasound. If appropriate, this is followed by fine-needle aspiration or needle-core biopsy. If the cytologic or histologic findings are not diagnostic, open surgical biopsy is usually undertaken for a definitive diagnosis.
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Breast Cancer in Ontario Both breasts are assessed for other lesions, both palpable and non-palpable. Bilateral synchronous cancers may occur in up to 3% of all cases (Ahearne et al. 1998). Treatment of breast cancer requires additional evaluation for the possibility of metastatic disease. A history and physical examination, chest x-ray and evaluation of serum liver enzymes are usually indicated. Additional scans and imaging are not usually warranted unless signs and symptoms are suggestive of metastatic disease. Removal and pathologic examination of the axillary lymph nodes is standard, as it provides accurate staging and prognostic information. Typically, breast cancer is staged using guidelines from the International Union Against Cancer (UICC) and the American Joint Committee on Cancer (AJCC). Based on clinical and pathologic assessment of tumour size and extension, involvement of regional lymph nodes and the presence or absence of distant metastases, this information is very important for subsequent treatment decisions and for estimating prognosis. While the OCR does not routinely collect stage information, past comparisons suggest that the stage distribution reported by the Surveillance, Epidemiology and End Results (SEER) system in the US is a reasonable approximation for Ontario, as shown in Table 3 (National Cancer Institute 1999; American Joint Committee on Cancer 1988). Table 3. Comparison of stage distribution1 in OCR2 versus SEER3 AJCC4 summary stage
OCR cases (1988-1991) n=150
SEER cases (1988-1991) n=52,324
SEER (1996) n=14,337
(%)
(%)
(%)
Stage I Stage II
39.1 38.5
40.9 38.7
46.6 35.0
Stage III Stage IV
8.6 10.1
6.1 5.1
6.8 4.5
Unknown
3.6
9.3
7.1
1
2 3 4
Cases are restricted to malignant breast cancer, as the first or only primary. OCR cases were derived from a recent Ontario-wide validation study Ontario Cancer Registry Surveillance, Epidemiology and End Results (US) American Joint Committee on Cancer
Treatment Breast cancer can be treated with surgery, radiation, chemotherapy or hormonal therapy. Treatment usually incorporates a combination of modalities, depending on the stage and type of cancer and the patient’s age and preferences. Canadian guidelines for the treatment of breast cancer are published in appropriate formats for women and for the professionals caring for them (The Steering Committee on Clinical Practice Guidelines for the Care and Treatment of Breast Cancer 1998). Breast cancer management guidelines developed by Cancer Care Ontario are available to professionals and the public through CCO’s website at www.cancercare.on.ca.
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Breast Cancer in Ontario Surgery is the primary treatment for breast cancer. This can be either a partial mastectomy (removing the tumour and a small margin of surrounding normal tissue) or a modified radical mastectomy (removing the entire breast). Long-term survival is similar after both types of surgery and there is some evidence of superior quality of life with partial mastectomy. In 1995-1996, approximately 62% of all Ontario women having surgery for breast cancer had partial mastectomies (sometimes called segmental mastectomy, lumpectomy, wide excision, tylectomy, quadrantectomy or breast conserving surgery). There is considerable geographic variation in breast conserving surgery rates, not only in Ontario, but also in the US and Europe (Iscoe et al. 1994). Systemic treatment with chemotherapy or tamoxifen has similar effects on recurrence and survival rates for both axillary node-negative and node-positive breast cancer. Tamoxifen is most effective in postmenopausal women, and chemotherapy in premenopausal women. Systemic treatment is usually recommended for women with node-positive disease because they have a high risk of recurrence, 75-80% over a 10-year period. Radiation therapy markedly reduces the risk of local recurrence when it is used as an adjuvant after breast conserving surgery. This radiation therapy requires daily outpatient treatments over five to six weeks. Radiation therapy is also useful for palliation in advanced cases of breast cancer, controlling symptoms associated with metastases. Prognosis Prognosis is closely related to stage of breast cancer at diagnosis. The US SEER system provides reasonable approximations of survival estimates following breast cancer in Ontario. Figure 3 shows the five-year relative survival rate by stage for cases diagnosed 1990-1991 (National Cancer Institute 1999). Figure 3. Five-year relative survival, by stage, for US SEER1 breast cancer cases, 1990-1991 100 90
Relative survival (%)
80 70 60 50 40 30 20 10 0 I
II
III
IV
Stage 1
Surveillance, Epidemiology and End Results (US)
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Breast Cancer in Ontario 1971-1996 Incidence and Mortality
Anna M Chiarelli Beth Theis Eric Holowaty Veronika Moravan E Diane Nishri October 2000
Surveillance Unit and The Ontario Breast Screening Program Division of Preventive Oncology Cancer Care Ontario
Breast Cancer in Ontario
Table of Contents Most common cancers and cancer causes of death ........................................................................... 1 Numbers of new cases and deaths .................................................................................................... 2 Trends in incidence and mortality ....................................................................................................... 3 Numbers of new cases and deaths, by age ........................................................................................ 4 Age-specific incidence and mortality ................................................................................................. 5 Trends in incidence, by age group ...................................................................................................... 6 Trends in mortality, by age group ....................................................................................................... 7
List of Tables Table 4.
Most common cancers diagnosed and cancer causes of death ........................................ 1 in Ontario females, 1992-1996
Table 5.
Ranking of breast cancer cases and deaths relative to other cancers ............................... 1 in Ontario women, by age group, 1992-1996
Table 6.
Annual percentage change (APC) for breast cancer incidence in Ontario, ...................... 6 by age group, 1971 -1996
Table 7.
Annual percentage change (APC) for breast cancer mortality in Ontario, ....................... 7 by age group, 1971-1996
List of Figures Figure 4.
Numbers of new cases of and deaths from breast cancer in Ontario, by year, ................. 2 1971-1996, and projected to 2000
Figure 5.
Age-standardized incidence and mortality rates (3-year moving averages) for ................. 3 breast cancer in Ontario, by year, 1971-1996
Figure 6.
Numbers of new cases of and deaths from breast cancer in Ontario, by age group, ......... 4 1992-1996
Figure 7.
Age-specific incidence and mortality rates for breast cancer in Ontario, .......................... 5 1992-1996
Figure 8.
Age-standardized incidence rates (3-year moving averages) for breast cancer ................ 6 in Ontario, by age group, 1971-1996
Figure 9.
Age-standardized mortality rates (3-year moving averages) for breast cancer ................. 7 in Ontario, by age group, 1971-1996
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Breast Cancer in Ontario
Most common cancers and cancer causes of death In 1992-1996, breast cancer was the commonest cancer diagnosed among Ontario women, representing 29% of the total cancers, and ranked first for every age group (Table 4, Table 5). Breast cancer was also the commonest cause of cancer death among Ontario women, accounting for 19% of all cancer deaths. However, in 1996, lung cancer passed breast cancer as the most common cause of cancer death among Ontario women. Table 4.
Most common cancers diagnosed and cancer causes of death in Ontario females1, 1992-1996
Rank Site
Cancer cases #
Rank Site
%
1
Breast
30,378
28.6
1
Breast
9,489
19.4
2 3 4 5
Colon/rectum Lung Corpus uteri Ovary
13,689 12,210 5,772 4,570
12.9 11.5 5.4 4.3
2 3 4 5
Lung Colon/rectum Ovary Pancreas
9,422 5,162 2,570 2,556
19.3 10.5 5.3 5.2
6
Non-Hodgkin’s lymphoma Melanoma Cervix Leukemia
4,109
3.9
6
1,875
3.8
2,995 2,897 2,819
2.8 2.7 2.7
7 8 9
Non-Hodgkin’s lymphoma Leukemia Stomach Brain
1,641 1,317 1,082
3.4 2.7 2.2
Pancreas
2,598
2.4
10
938 12,884
1.9 26.3
48,936
100.0
7 8 9 10
All other sites Total 1
%
Cancer deaths #
24,051
22.7
106,088
100.0
Multiple myeloma All other sites Total
Non-melanoma skin cancer is not included as it is not recorded in the OCR
Table 5.
Ranking of breast cancer cases and deaths relative to other cancers in Ontario women, by age group, 1992-1996 Cases
Deaths
#
%1
Rank
1 1
1,923 5,330
24.9 43.7
1 1
340 1,062
27.8 33.5
50-69
1
13,390
32.0
2
3,708
21.4
70+
1
9,718
22.5
2
4,376
16.2
Age group
Rank
20-39 40-49
1
#
%1
Percentage of all cancers or cancer deaths in the age group
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Breast Cancer in Ontario
Numbers of new cases and deaths In the year 2000, approximately 7,200 women in Ontario will be diagnosed with breast cancer. The number of new cases of breast cancer diagnosed annually in Ontario increased by about 3,000 or 113% between 1971 and 1996 (Figure 4). This increase is mainly due to population growth and population aging, rather than an increase in the underlying risk. In the year 2000 approximately 2,000 Ontario women will die from breast cancer. The number of breast cancer deaths per year also increased over this time period (1971 to 1996) by about 900 cases or about 88%. The number of deaths per year has increased more slowly than the number of new cases. This reflects the steady improvements in survival seen over this time period. Figure 4. Numbers of new cases of and deaths from breast cancer in Ontario, by year, 1971-1996, and projected to 2000 8000
Number of new cases/deaths
7000
Cases - - - - - Projected number
6000 5000 4000 3000 Deaths
2000 1000 0 1971
1976
1981
1986
1991
1996
Y e a r of diagnosis/death
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Breast Cancer in Ontario
Trends in incidence and mortality Age-standardized incidence rates for breast cancer increased slowly but steadily from 1971 to 1996 by about 15 per 100,000 or 17% (Figure 5). (Rates are age standardized to the 1991 Canadian population, Appendix A.) This increase may be due, in part, to the rising number of screening mammograms since the mid-1980s and may also be affected by reproductive histories (National Cancer Institute of Canada 2000). In contrast, age-standardized mortality rates have increased only slightly from 1971 to 1986 (4% increase). Since 1986, mortality has been declining. Between 1986 and 1996 breast cancer mortality in Ontario decreased by about 3 per 100,000 or 9%. This decrease may be due both to improvements in treatment and to the early detection of breast cancers by screening. Figure 5. Age-standardized incidence and mortality rates (3-year moving averages) for breast cancer in Ontario, by year, 1971-1996
Age-standardized rate per 100,000
120
100
Incidence
80
60
40 Mortality 20
0 1971
1976
1981
1986
1991
1996
Year of diagnosis/death
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Breast Cancer in Ontario
Numbers of new cases and deaths, by age The number of newly diagnosed cases increased with age to a peak in the 65-69 age group (Figure 6). The number of breast cancer deaths also increased steadily with age to a peak in the 70-74 age group. Numbers of deaths are considerably less than numbers of new cases in every age group, largely because of the favorable prognosis among the majority of new cases. Figure 6. Numbers of new cases of and deaths from breast cancer in Ontario, by age group, 1992-1996 4000
Number of new cases
Number of new cases/deaths
3500
Number of deaths
3000 2500 2000 1500 1000 500 0 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85+ Age at diagnosis/death
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Breast Cancer in Ontario
Age-specific incidence and mortality Breast cancer is very uncommon in women aged less than 30 years and then increases steadily to a peak in the 75-79 age group (Figure 7). Deaths from breast cancer are very uncommon in women aged less than 35 years, but then increase steadily from that age. Figure 7. Age-specific incidence and mortality rates for breast cancer in Ontario, 1992-1996 400 Incidence
Age-specific rate per 100,000
350 300
Mortality
250 200 150 100 50 0 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 85+ A ge at diagnosis/death
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Breast Cancer in Ontario
Trends in incidence, by age group For younger women (20-49) incidence rates decreased during the earlier part of the time period (1971-1981) and increased slightly for the later part of the time period (Figure 8, Table 6). This increase may be explained by changes in reproductive histories. For women over 50 years of age incidence rates have increased over the time period, particularly after 1986. This pattern is consistent with the increased use of mammography as a screening test in Canada around this time (National Cancer Institute of Canada 2000). Figure 8. Age-standardized incidence rates (3-year moving averages) for breast cancer in Ontario, by age group, 1971-1996 400 70+
Age-standardized rate per 100,000
350 300
50-69 250 200 150
40-49
100 50 20-39 0 1971
1976
1981
1986
1991
1996
Year of diagnosis
Table 6.
Annual percentage change (APC) for breast cancer incidence in Ontario, by age group, 1971-1996 Age group
Period
APC (%)
20-39
1971-1977
-2.2
40-49
1978-1996 1971-1981
0.7 -1.2
50-69
1982-1996 1971-1996
0.6 1.4
70+
1971-1996
0.9
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Breast Cancer in Ontario
Trends in mortality, by age group Breast cancer mortality rates have been declining for women aged 40-49 since 1971 (Figure 9, Table 7). Mortality rates have been decreasing for women 50-69 since 1989. It is likely that both screening and improved treatments have contributed to this decline. Mortality rates are stable in women under age 40 and are increasing steadily in women age 70 and older. Figure 9. Age-standardized mortality rates (3-year moving averages) for breast cancer in Ontario, by age group, 1971-1996 180 70+
Age-standardized rate per 100,000
160 140 120 100 80
50-69
60 40 40-49 20 20-39 0 1971
1976
1981
1986
1991
1996
Year of death
Table 7.
Annual percentage change (APC) for breast cancer mortality in Ontario, by age group, 1971-1996 Age group
Period
APC (%)
20-39
1971-1996
0.0
40-49 50-69
1971-1996 1971-1988
-1.5 0.4
1989-1996
-2.7
1971-1996
0.9
70+
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Breast Cancer in Ontario 1971-1996 Geographic Patterns
Anna M Chiarelli Beth Theis Eric Holowaty Veronika Moravan E Diane Nishri October 2000
Surveillance Unit and The Ontario Breast Screening Program Division of Preventive Oncology Cancer Care Ontario
Breast Cancer in Ontario
Table of Contents International comparisons .................................................................................................................. 1 Interprovincial comparisons ............................................................................................................... 2 Ontario comparisons .......................................................................................................................... 3
List of Tables Table 8.
Age-standardized incidence and mortality rates (per 100,000), rate ratios (RR) ............... 3 and 95% confidence intervals (CI) for breast cancer, by CCOR, 1992-1996
Table 9.
Age-standardized incidence rates (per 100,000), rate ratios (RR) and 95% ...................... 4 confidence intervals (CI) for breast cancer, by Public Health Unit, 1992-1996
Table 10.
Age-standardized mortality rates (per 100,000), rate ratios (RR) and 95% ....................... 6 confidence intervals (CI) for breast cancer, by Public Health Unit, 1992-1996
List of Figures Figure 10. Age-standardized incidence rates for breast cancer, by country/region, 1988-1992 .......... 1 Figure 11. Age-standardized incidence and mortality rates for breast cancer ................................... 2 in Canada, 1991-1995 Figure 12. Age-standardized incidence rates for breast cancer, by Public Health Unit, ..................... 5 1992-1996 Figure 13. Age-standardized mortality rates for breast cancer, by Public Health Unit, ...................... 7 1992-1996
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Breast Cancer in Ontario
International comparisons Breast cancer rates vary dramatically around the world. Figure 10 provides examples from some cancer registries with reporting methods similar to Ontario. Breast cancer is generally much commoner in developed countries and lower in developing countries. Breast cancer rates in Ontario (and Canada) are among the highest in the world. These variations are probably due to differences in reproductive patterns, diet, body size and hormone levels. Figure 10. Age-standardized incidence rates1 for breast cancer, by country/region, 1988-1992 USA, SEER White USA, SEER Black Canada, Ontario UK, Oxford The Netherlands Sweden UK, Scotland Australia, New South Wales Italy, Florence Finland Slovakia US, Puerto Rico Colombia, Cali Hong Kong India, Bombay China, Tianjin Japan, Osaka Thailand, Chiang Mai
0
10
20
30
40
50
60
70
80
90
100
Age-standardized rate per 100,000 1
Standardized to the World Standard population
Cancer Care Ontario
1
Breast Cancer in Ontario
Interprovincial comparisons There is some variation in breast cancer incidence and mortality rates across Canada (Figure 11). Ontario’s incidence and mortality rates for the period 1991-1995 were similar to the Canadian rates, which were 101.8 per 100,000 for incidence and 29.6 per 100,000 for mortality. In theory, it should be possible to draw inferences about the effectiveness of treatment from the relative levels of incidence and mortality between provinces. This type of analysis should only be undertaken with great caution, however, because of the differences in cancer incidence reporting procedure used by provincial cancer registries. Figure 11. Age-standardized1 incidence and mortality rates for breast cancer in Canada, 1991-1995 2 Newfoundland
Incidence
Prince Edward Island
Mortality
Nova Scotia New Brunswick Quebec Ontario Manitoba Saskatchewan Alberta British Columbia
0
20
40
60
80
100
120
Age-standardized rate per 100,000 1 2
Standardized to the 1991 Canadian population For Quebec, incidence data are for 1991-1994
Cancer Care Ontario
2
Breast Cancer in Ontario
Ontario comparisons Age-standardized incidence rates for 1992-1996 ranged from 97.6 and 97.7 per 100,000 in the Southwest and South Cancer Care Ontario Regions (CCORs), respectively, to 106.7 in the Eastern CCOR, only a 9% difference (Table 8). (Definitions of the CCORs are found in Appendix B.) Mortality showed a broader range, with the highest rate in the Central West CCOR, at 32.3 per 100,000 and the lowest mortality rate in the Northwest CCOR, at 26.0 per 100,000. Table 9 and Figure 12 present the age-standardized incidence rates for Ontario’s 37 Public Health Units (PHUs) for the time period 1992-1996. (Definitions of the PHUs are found in Appendix C.) Incidence rates ranged from a high of 112.2 per 100,000 in North Bay and District to a low of 71.9 in Huron, a 56% difference. Table 10 and Figure 13 present age-standardized mortality rates by PHU for 1992-1996. Rates ranged from a high of 36.3 per 100,000 in Leeds-Granville-Lanark to a low of 22.6 per 100,000 in Lambton. Drawing conclusions about differences in incidence and mortality patterns must be done with caution. Survival rates for breast cancer are high compared with other cancers; this increases the possibility that women may reside in a different area at their time of death than when they are diagnosed. Table 8.
Age-standardized1 incidence and mortality rates (per 100,000), rate ratios2 (RR) and 95% confidence intervals (CI) for breast cancer, by CCOR, 1992-1996 Incidence
CCOR
RR
95% CI
#
Rate
RR
95% CI
1.07* 1.02 0.99 1.00
(1.04, 1.11) (0.98, 1.07) (0.97, 1.00) (0.97, 1.03)
983 665 4,053 1,355
31.4 31.7 29.2 32.3
1.04 1.05 0.97* 1.07*
(0.98, 1.11) (0.97, 1.14) (0.94, 1.00) (1.02, 1.13)
97.6 97.7 97.9
0.98 0.98 0.99
(0.95, 1.01) (0.92, 1.05) (0.94, 1.03)
1,355 331 531
29.5 31.7 30.7
0.98 1.05 1.02
(0.93, 1.03) (0.94, 1.17) (0.93, 1.11)
683 102.5
1.03
(0.96, 1.11)
178
26.0
0.86*
(0.74, 1.00)
All Ontario3 30,097 99.3
1.00
Eastern Southeast Central East Central West Southwest South Northeast Northwest
#
Rate
Mortality
3,196 106.7 2,015 101.2 13,409 97.9 3,921 98.9 4,226 984 1,663
9,451 30.1
1.00
1
Standardized to the 1991 Canadian population Ratio of the incidence or mortality rate in a CCOR to that for all Ontario (known residence only) 3 Excludes cases and deaths with unknown residence * Significantly different from 1.0 (p
