BACKGROUND

Breast cancer continues to be the most common cancer among Canadian women and the second highest cause of cancer death in women, with 19,200 new cases and 5,500 deaths estimated for 2000¹. A rise in the incidence of breast cancer has been observed over several decades paralleling an increase in mammographic screening. However, mortality rates have dropped, particularly since 1990, attributed, in part, to improved treatment and to early detection through mammography screening (Figure 1).

Figure 1 Age-standardized incidence and mortality rates for breast cancer in Canada, 1980-2000

Source: National Cancer Institute of Canada: Canadian Cancer Statistics 2000, Toronto, Canada, 2000. Notes: Mortality rates for 1998-2000 and incidence rates for 1996-2000 are estimates. Rates are standardized to age distribution of 1991 population.

Currently, there is insufficient knowledge about the causes of breast cancer for primary prevention strategies to reduce incidence in the population. Most known risk factors are not modifiable. Of the known risk factors, age has the strongest influence. Both the incidence and mortality of breast cancer rise sharply with age, with the highest rates among women aged 60 and over². Nearly half of all new cases occur among women aged 50 to 69¹. It has been demonstrated, through randomized trials, that women in this age group benefit the most from breast screening. Delivery of regular, high quality breast screening to this group has the potential to reduce breast cancer mortality rates by approximately one third^3,4.

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