Racial/Ethnic Differences in Diagnosis of Breast Cancer at Stage I and Subsequent Survival Reflect Biologic Differences


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Javaid Iqbal, MD

Among U.S. women diagnosed with invasive breast cancer, the likelihood of diagnosis at an early stage, and survival after stage I diagnosis, varied by race and ethnicity. Much of the difference could be statistically accounted for by intrinsic biological differences such as lymph node metastasis, distant metastasis, and triple-negative behavior of tumors.

—Javaid Iqbal, MD, Steven A. Narod, MD, FRCPC, and colleagues

In a study reported in JAMA, Javaid Iqbal, MD, of Women’s College Research Institute, Toronto, and colleagues found racial/ethnic differences in the likelihood of breast cancer diagnosis at stage I and subsequent survival in U.S. breast cancer patients.1 These differences seemed largely to reflect intrinsic biologic differences.

Study Details

The observational study involved data on 373,563 women diagnosed with invasive breast cancer from 2004 to 2011 in the Surveillance, Epidemiology, and End Results (SEER) 18 registries database. The racial/ethnic distribution of patients was 268,675 non-Hispanic white (71.9%), 34,928 Hispanic (9.4%), 38,751 black (10.4%), 4,937 Chinese (1.3%), 3,751 Japanese (1.0%), 2,191 South Asian (0.6%), 14,332 other Asian (3.8%), and 5,998 other ethnicity (1.6%).

Biologic aggressiveness (distant metastases, lymph node metastases, triple-negative cancer) of small-sized tumors (≤ 2.0 cm) was estimated for each of the eight racial/ethnic groups; odds ratios (ORs) for being diagnosed at stage I compared with a later stage and hazard ratios (HRs) for death after stage I diagnosis were determined. Follow-up was conducted through December 31, 2011, with a mean follow-up of 40.6 months (median, 38 months).

Diagnosis at Stage I

On multivariate analysis including age, annual income, estrogen receptor (ER) status, and race/ethnicity, compared with non-Hispanic white women (50.8%), diagnosis at stage I was significantly more likely among Japanese women (56.1%, OR = 1.23, P < .001) and significantly less likely (all P < .001) among Hispanic women (40.1%, OR = 0.71), black women (37.0%, OR = 0.65), South Asian women (40.4%, OR = 0.73), other Asian women (45.2%, OR = 0.85), and women of other race/ethnicity (43.6%, OR = 0.78); the odds ratio for Chinese women (50.1%) was 1.04 (P = .24).

Aggressiveness of Small Tumors

With regard to aggressiveness characteristics of tumors ≤ 2.0 cm, node-positive disease was present in 24.1% of black patients, 23.3% of Hispanic patients, 23.2% of South Asian patients, 20.2% of patients with “other” ethnicity, 18.6% of “other” Asian patients, 18.4% of non-Hispanic white patients, 18.1% of Chinese patients, and 14.6% of Japanese patients. The rate of node-positive disease was significantly higher in black women and significantly lower in Japanese women vs non-Hispanic white women (both P < .001).

Distant metastases were present in 1.5% of black women (P < .001 vs non-Hispanic white women); 1.2% of Hispanic and South Asian women; 1.0% of non-Hispanic white women; and 0.8% of Chinese, Japanese, and “other” Asian women and women of  “other” ethnicity.

Black women (73.6%) had the lowest frequency of ER-positive disease. ER-positive disease was present in 88.5% of Japanese women, 86.1% of non-Hispanic white women, 83.8% of Chinese women, 82.4% of South Asian women, and 82.6% of Hispanic women.

Black women had the highest rate of triple-negative disease (17.2%). Triple-negative breast cancer was present in 10.4% of South Asian women, 10.0% of Hispanic women, 8.8% of Chinese women, 8.2% of Japanese women, and 8.0% of non-Hispanic white women.

Survival in Stage I Disease

Overall, the 7-year actuarial breast cancer survival among women with stage I disease was 96.8%, including 98.6% for Japanese women, 98.2% for Chinese women, 97.0% for non-Hispanic white women, 96.5% for Hispanic women, and 93.9% for black women. On multivariate analysis, 7-year actuarial risk of death from stage I breast cancer was highest for black women (6.2%) and significantly higher than the risk among non-Hispanic/Hispanic white women (3.0%; HR = 1.57, P < .001).

A similar increased risk for black vs non-Hispanic/Hispanic white women was seen after excluding women with triple-negative disease (4.6% vs 2.4%, age-adjusted HR = 1.73, P < .001). All Asian women combined had a lower risk (1.9%) vs non-Hispanic/Hispanic white women (HR = 0.60, P < .001).

Among all women with tumors ≤ 2.0 cm, 7-year actuarial survival was 95.1%. The actuarial probability of death due to such tumors was significantly higher for black women vs non-Hispanic white women (9.0% vs 4.6%, HR = 1.96, P < .001), with the increased risk persisting after adjustment for age, income, and ER status (HR = 1.56, P < .001), age and ER status alone (HR = 1.53, P < .001), and age and income alone (HR = 1.86, P < .001).

The investigators concluded: “Among U.S. women diagnosed with invasive breast cancer, the likelihood of diagnosis at an early stage, and survival after stage I diagnosis, varied by race and ethnicity. Much of the difference could be statistically accounted for by intrinsic biological differences such as lymph node metastasis, distant metastasis, and triple-negative behavior of tumors.”

Steven A. Narod, MD, FRCPC, of Women’s College Research Institute, is the corresponding author for the JAMA article. ■

Disclosure: The authors reported no potential conflicts of interest.

Reference

1. Iqbal J, Ginsburg O, Rochon PA, et al: Differences in breast cancer stage at diagnosis and cancer-specific survival by race and ethnicity in the United States. JAMA 313:165-173, 2015.

Melanie E. Royce, MD, PhD, of the University of New Mexico Cancer Center, offers a closer look at the disparities in breast cancer outcome by race and ethnicity.


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