Epidemiology of breast cancer in Connecticut women.

At least 50% of breast cancer may be "explained" by known or suspected risk factors, including modifiable behaviors involving diet, overweight, exercise, and alcohol use. Interest continues to grow in "hereditary" breast (and ovarian) cancer due to germ cell mutations, but most breast cancers are due to environmentally induced (somatic) mutations. According to data from the Connecticut Tumor Registry, the incidence of invasive breast cancer has changed little since 1990. The proportion of breast cancers diagnosed at the in situ stage has increased while the proportions diagnosed at the regional and distant stages have decreased, which is consistent with an effect of increased screening. Breast cancer mortality rates, the crucial yardstick of progress in cancer control, have declined slightly in Connecticut (and nationally) since 1989, reflecting the effects of earlier detection (through screening) and improved treatment. Primary care physicians have an important role in primary and secondary prevention.