Prior mammography utilization: Does it explain Black-White differences in breast cancer outcomes?
Black women are more likely to be diagnosed with advanced stage breast cancer and experience worse survival than whites possibly because blacks receive fewer mammograms. To investigate whether regular mammography use can explain the observed black-white difference in stage at diagnosis and survival, we undertook a study using the Linked Medicare-Tumor Registry Database The study sample included black and white women age $\ge$67 diagnosed with breast cancer, from 1987-1989, in three Surveillance, Epidemiology, and End Results tumor registries. Women were classified based on their mammography use during the 2 years before diagnosis: nonusers (no prior mammograms), regular users (at least 2 mammograms at least 10 months apart), or peri-diagnosis users (only mammogram(s) within 3 months before diagnosis). Stage was classified as early (in situ/local) or late (regional/distant). Women whose mammography use could not be categorized (n = 292) or whose disease was unstaged (n = 141) were excluded Mean age at diagnosis for the 4,005 women was 76, 4% were black, 37% married, and 16% lived in an area with a median income $<$ $15,000; 48\% resided in Connecticut, 35\% in Seattle, and 17\% in Atlanta. One-quarter (23\%) of women were nonusers, 19\% regular users, and 58\% peri-diagnosis users of mammography. One-third of women were diagnosed with late-stage disease. Blacks were more likely to be nonusers of mammography (OR = 3.0, 95\% CI 2.4--3.8) and were more likely to be diagnosed with late-stage disease (OR = 2.5, 95\% CI 1.6--4.0) than whites. This black-white difference is related to mammography use in that blacks who were nonusers were significantly more likely to be diagnosed with late-stage disease than black regular users (OR = 6.7, 95\% CI 1.8--27.4); and that blacks and whites who were users were diagnosed at a similar stage (OR = 1.05, 95\% CI 0.3--3.4). Prior mammography use explained nearly 30\% of the excess late-stage disease among blacks. Blacks experienced a higher risk of death relative to whites (RR = 1.5, 95\% CI 1.1--2.1). Prior mammography use reduced the estimated relative risk of black race to (RR = 1.3, 95\% 0.9--1.8) Black women benefit from regular mammography use by being diagnosed with earlier stage disease. These findings suggest that differences in breast cancer outcomes is not strongly linked to race, but is rather an issue of whether a woman receives regular mammograms