Oct. 8, 1997 In the past few years, the number of women dying from breast cancer declined almost five per cent, the largest short-term decrease since 1950, according to a recent paper in Cancer Prevention & Control.
"Physicians are now detecting smaller, localized tumors earlier," says Professor Judy-Anne Chapman, a biostatistician at U of T, the Henrietta Banting Breast Centre and Women's College Hospital, who oversaw the analytical review of 153 breast cancer studies.
Reviewing papers for the National Cancer Institute of Canada, Chapman and her associates looked at studies examining breast cancer rates, screening and treatment conducted over the past 50 years. Data from U.S. studies revealed the incidence of breast cancer between 1940 and 1982 increased one per cent each year. Between 1982 and 1987, the increase was about four per cent each year.
But while the incidence of breast cancer has increased, the number of women dying from breast cancer is decreasing. Between 1989 and 1992, the mortality rate declined 4.7 per cent. "Through screening methods, particularly mammography, breast cancer is being detected earlier," notes Chapman. "Earlier detection has improved the prognosis for survival.
"As more breast cancers are detected at an earlier stage, mortality rates should continue to decline," she says. "While mammography is recommended for Canadian women 50 to 69 years of age, public health decision-makers need to revisit the question of whether 40- to 49-year-old women would also benefit from breast cancer screening."
Chapman notes that a review of data from the past 50 years needs to take into account the following cohort effects: women aged 40 to 49 more than 20 years ago have a relatively lower risk of breast cancer compared to current and future cohorts of 40- to 49-year-old women. This is due to that fact that fewer women 20 years ago were never pregnant, they tended to have their first pregnancy earlier and they had more pregnancies. In comparison, women currently 40 to 49 years of age may be at a higher risk of breast cancer because more of them have never been pregnant and there is a greater tendency to delay the first pregnancy and have fewer pregnancies.
The data analysis also revealed physicians play a key role in mammography. "Ninety-three to 94 per cent of women will comply with a physician's request to have a mammogram," says Chapman. The paper's investigators were funded by the National Cancer Institute of Canada and the Canadian Cancer Society
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