Regional variations in breast cancer incidence among California women, 1988-1997.

Background: Internationally, California has some of the highest breast cancer rates; these rates also show substantial regional variations within the state. This study describes geographic breast cancer incidence patterns within California and evaluates the degree to which socioeconomic status (SES) and urbanization explain the regional variability.

Methods: Invasive breast cancer cases in women > or =20 year of age were identified from the California Cancer Registry, for 1988-1997, then assigned to one of three regions (San Francisco Bay Area, Southern Coastal Area and the rest of California), based on residence at diagnosis.