Breast Cancer

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In Canada today, one woman in nine can expect to develop breast cancer during her lifetime and one in 25 will die from the disease. In 1999, it is estimated that 18 700 cases will be diagnosed. While lung cancer has now surpassed breast cancer as the leading cause of cancer deaths in women, 5400 women will likely die due to breast cancer in 1999. Accounting for close to 30% of all new cancer cases each year, it is still one of the most frequently diagnosed cancers in Canadian women.

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A number of the general features of breast cancer statistics are provided in:

• Breast Cancer Risk Factors, Prevention and Trends

Regional variations in breast cancer incidence across Canada are illustrated using maps of incidence rates and ratios. As much as possible, these two maps should be examined together.

Risk Factors, Prevention and Trends

The cause of breast cancer is unknown and it cannot be prevented. Other than being a woman, the most significant risk factor associated with breast cancer is aging. What a bitter irony! As life expectancy rises so too does the chance of getting breast cancer.

Health Canada lists the following additional risk factors:

• family history of breast cancer
• a history of cancer in one breast
• history of certain types of benign breast disease and high levels of radiation exposure to the chest
• obesity in postmenopausal women
• various reproductive risk factors, such as:
• never having had children being 30 or more years of age at first full-term pregnancy
• having an early onset of menstruation and a late onset of menopause
• various demographic factors, such as: living in an urban area
• belonging to a higher socioeconomic class
• being born in North America or Northern Europe

Early detection is the best way of saving lives. "At present, the only proven strategy to reduce breast cancer deaths is early detection through mammography in women aged 50 to 69. There is clear evidence from population-based trials that mammographic screening can reduce mortality from breast cancer by approximately 30% in women aged 50 to 69" (Health Canada).

Currently, mammograms are recommended every two years for women 50 to 69 years of age. Unfortunately, while from 1990 to 1997 there has been a "dramatic increase of 28 percentage points in the proportion of women age 50 and older who have ever had a mammogram", the increase in the proportions of women who have had a mammogram within the past two years has been modest (Federal, Provincial and Territorial Advisory Committee on Population Health (1999); Snider et al. (1966)).

Breast cancer has risen steadily during the past 30 years, particularly in the last decade (Figure 1). The latter increase is partially due to more effective detection methods. Early detection and improved treatment techniques have resulted in significantly fewer deaths.

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Figure 1. Breast and Lung Cancer Incidence and Mortality Rates, 1970 to 1999

The declining mortality rate for breast cancer stands in stark contrast to the increasing mortality rate for lung cancer for women. The incidence and mortality rates for both of these cancers have been placed on this same graph to illustrate the differences that Canadian women are experiencing with these two diseases.