Ethnic Differences in Breast Cancer Survival Due to Biology
[This study] lends support to the argument that there are variations in the intrinsic biology of tumors based on racial/ethnic background.
In the United States, the likelihood of a woman being diagnosed with early-stage breast cancer and her survival after such a diagnosis varies by race and ethnicity. These differences can largely be explained by intrinsic tumor biology, according to a study published online January 13 in JAMA.
“It has been conventional wisdom that differences in outcomes for cancer patients who are black and white may be explained by differences in patterns of care, including access to care,” said lead author Steven Narod, MD, FRCPC, from the Cancer Research Institute at Women’s College Hospital in Toronto. “This may be true for some cancers, but for small-sized breast cancers it does not seem to be an adequate explanation.”
The team found that black women are less likely to be diagnosed with early-stage small-sized breast cancer than white women, and twice as likely to die from this form of breast cancer.
In the study, 7-year survival for small breast cancer was “very good,” according to Dr Narod; it was 98% in Japanese women, 97% in white women, and 91% in black women. However, variation in survival between women exists, and can be explained by inherent biologic differences in the cancer and, equally important, the woman’s ethnicity, he added.
“By focusing only on disparities in healthcare and health services, we are potentially going to miss a very important line of study,” Dr Narod pointed out. The distribution of healthcare and intrinsic biologic differences “should be pursued,” he added. “In the future, it may be that ethnic background will be taken into account when deciding on a particular treatment for particular patients.”
Dr Narod and colleagues used the Surveillance, Epidemiology, and End Results (SEER) 18 registries database, which covers about 28% of the population in the United States. They identified women diagnosed with small-sized (2.0 cm or less) stage I breast cancer from 2004 to 2011, and looked at biologic aggressiveness (triple-negative cancers, lymph node metastases, and distant metastases) in eight racial/ethnic groups. Then they estimated whether racial differences were related to inherent differences in tumor aggressiveness or earlier detection.
The analysis involved 373,563 women who were followed for a mean of 40.6 months; 71.9% of the cohort was Non-Hispanic white, 10.4% was black, 9.4% was Hispanic, 6.7% was Asian, and 1.6% was other.
Table. Diagnosis of Stage I Small Breast Cancer
95% Confidence Interval
At 7 years, the actuarial risk for death from stage I breast cancer was higher in black women than non-Hispanic white women (6.2% vs 3.0%; hazard ratio [HR], 1.57; 95% confidence interval [CI], 1.40 -1.75; P < .001). This relation remained after women with triple-negative disease were excluded from the analysis (HR, 1.73; 95% CI, 1.50 – 2.00; P < .001). However, the 7-year actuarial risk for death was lower in South Asian women (1.7%; HR, 0.48; 95% CI, 0.20 – 1.15; P < .10).
The probability of dying from small-sized breast cancer was higher in black women than in non-Hispanic white women (9.0% vs 4.6%; HR, 1.96; 95% CI, 1.82 – 2.12; P < .001). This higher probability remained after adjustment for age, income, and estrogen-receptor (ER) status (HR, 1.56; 95% CI, 1.45 – 1.69; P < .001).
The probability of nodal metastases was higher in black women than non-Hispanic white women (24.1% vs 18.4%; P < .001), as was the probability of distant metastases (1.5% vs 1.0%; P < .001).
The proportion of ER-positive tumors was lower in black women than in Japanese or non-Hispanic white women (73.6% vs 88.5% vs 86.1%). In addition, black women had the highest proportion of triple-negative breast cancers (17.2%).
Even though much progress has been made in reducing deaths from breast cancer, black women still die at higher rates from more aggressive forms of the disease, note Bobby Daly, MD, MBA, and Olufunmilayo Olopade, MBBS, FACP, both from the University of Chicago, in an accompanying editorial.
This study “is significant in that it makes progress in explaining the racial survival disparity in breast cancer, [and] lends support to the argument that there are variations in the intrinsic biology of tumors based on racial/ethnic background,” said Dr Daly.
Decreasing financial and administrative barriers to minority enrolment in clinical trials could increase our understanding of the biologic differences in survival, Dr Daly explained. In addition, increased referrals of minority women to cancer risk clinics could lead to better risk-assessment models and more data on genetic variants in black women.
“We need system-wide reforms to address the delays, misuse, and underuse of treatment for minority women with breast cancer, as this suboptimal care is of increased importance in the setting of more aggressive tumors,” he said. Because the United States has an ethnically diverse population, “beyond biology, we should also look into cultural practices and level of health literacy in immigrant populations,” he added.
JAMA. 2015;313:141-142, 165-173.