Marilyn Schneider, Ph.D.
Canadian Breast Cancer Research Initiative
Breast cancer is, in large part, a disease of aging in women. It is a disease of genes gone awry. Although a small proportion of women are born with an inherited mutant BRCA1 or BRCA2 gene that immediately puts them at very high risk for breast cancer, these inherited mutations account for only 5-10% of breast cancer cases. In most breast cancers, the woman accumulates sporadic gene mutations throughout her lifetime, and when appropriate combinations of these mutations accumulate in the woman's breast cell, she has the beginning of a breast cancer tumour.
One out of every 9.5 Canadian women is now expected to develop breast cancer sometime in her lifetime. This, however, is the lifetime risk, and this risk is known to increase with age. What is more relevant to an older woman is the probability that she will develop breast cancer over the next decade. A 60-year-old woman's probability of getting breast cancer before age 70 is 2.9% or 1 in 34; a 70-year-old woman's probability is 3.2% or 1 in 31.1 Breast cancer is primarily a disease of older women, with only 22% of breast cancer cases occurring in women under age 50, 45% occurring in women aged 50-69, and 32% occurring in women aged 70 and over.2
On the one hand, the incidence of breast cancer has risen slowly but steadily over the past three decades, particularly for those women aged 50-69 and over the age of 70.