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Breast Cancer Diagnoses and Survival Vary by Race, Ethnicity

Intrinsic biologic differences account for variations, study finds

Among nearly 375,000 U.S. women diagnosed with invasive breast cancer, the likelihood of diagnosis at an early stage and of survival after stage-I diagnosis varied by race and ethnicity, with much of the difference accounted for by biologic variations, according to a study in the January 13 issue of JAMA.

In the U.S., incidence rates of breast cancer among women vary substantially by racial or ethnic group. Race/ethnicity and sociodemographic factors may influence a woman’s adherence to recommendations for clinical breast examinations, breast self-examination, or screening mammogram and the likelihood of her seeking appropriate care in the event that a breast mass is noticed. A growing body of evidence suggests that biologic factors may also be important in determining the stage at diagnosis (i.e., the growth rate and metastatic potential of small breast cancer tumors may vary between women due to inherent differences in grade and other or unknown pathologic features), according to background information in the article.

Javaid Iqbal, MD, of Women’s College Hospital, Toronto, and colleagues examined the proportion of breast cancers that were identified at an early stage (stage I) in different racial or ethnic groups in the U.S. and whether ethnic differences may be better explained by early detection or by intrinsic biologic differences in tumor aggressiveness.

The study included women diagnosed with invasive breast cancer from 2004 to 2011 who were identified in the Surveillance, Epidemiology, and End Results (SEER) registries database (N = 452,215). For each of eight racial/ethnic groups, biologic aggressiveness (triple-negative cancers, lymph node metastases, and distant metastases) of small tumors of 2.0 cm or less was estimated. In addition, the odds were determined for being diagnosed at stage I compared with a later stage, as was the risk of death from stage-I breast cancer according to the patient’s racial or ethnic group.

Of 373,563 women with invasive breast cancer, 268,675 (71.9%) were non-Hispanic white; 38,751 (10.4%) were black; 34,928 (9.4%) were Hispanic white; 25,211(6.7%) were Asian; and 5,998 (1.6%) were other ethnicities. The average follow-up period was 40.6 months. The researchers found that Japanese women were significantly more likely to be diagnosed at stage I (56.1%) compared with non-Hispanic white women (50.8%), whereas black women were less likely to be diagnosed at stage I (37.0%) than were women of South Asian ethnicity (i.e., Asian Indian and Pakistani) (40.4%).

The 7-year actuarial risk for death from stage-I breast cancer was highest for black women (6.2%) compared with white women (3.0%); the risk was only 1.7% for South Asian women. The probability of a woman dying from small breast cancer tumors (2.0 cm or less) was significantly higher for black women (9.0%) compared with non-Hispanic white women (4.6%).

The authors write that much of the difference in diagnosis and survival could be statistically accounted for by intrinsic biologic differences, such as lymph-node metastasis, distant metastasis, and the triple-negative behavior of tumors.

Source: JAMA Network; January 13, 2015.

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