The likelihood of diagnosing invasive breast cancer at an early stage, and survival after stage I diagnosis, varied by race and ethnicity, with much of the difference accounted for by biological differences, according to researchers at the Women's College Hospital, Toronto.
Researchers studied nearly 375,000 women in United States who were diagnosed with invasive breast cancer from 2004 to 2011 who were identified in the Surveillance, Epidemiology, and End Results (SEER). They examined the proportion of breast cancers that were identified at an early stage (stage I) in different racial/ethnic groups in the US and whether ethnic differences may be better explained by early detection or by intrinsic biological differences in tumor aggressiveness.
For each of 8 racial/ethnic groups, biological aggressiveness of small-sized tumors of 2 cm or less was estimated. Scientists determined the odds of being diagnosed at stage I compared with a later stage, and the risk of death from stage I breast cancer by racial/ethnic group.
They found that 268 675 (71.9 percent) women from the study group were non-Hispanic white, 34,928 (9.4 percent) were Hispanic white, 38,751 (10.4 percent) were black, 25,211(6.7 percent) were Asian, and 5,998 (1.6 percent) were of other ethnicities. Researchers found that Japanese women were significantly more likely to be diagnosed at stage I (56.1 percent) than non-Hispanic white women (50.8 percent), while black women were less likely to be diagnosed at stage I (37.0 percent), and also women of South Asian ethnicity (Asian Indian, Pakistani) (40.4 percent).
The 7-year actuarial risk for death from stage I breast cancer was highest among black women (6.2 percent) compared with white women (3.0 percent), while it was 1.7 percent for South Asian women. The probability of a woman dying due to small-sized breast cancer tumors was significantly higher among black women (9.0 percent) compared with non-Hispanic white women (4.6 percent).
Researchers concluded that race/ethnicity and socio-demographic factors may influence a woman's adherence to recommendations for clinical breast examination, breast self-examination, or screening mammogram and the likelihood of her seeking appropriate care in the event that a breast mass is noticed. The findings also suggest that biological factors may also be important in determining stage at diagnosis i.e. the growth rate and metastatic potential of small-sized breast cancer tumors may vary between women due to inherent differences in grade and other or unknown pathological features.
The study appears in JAMA.