Variation in Breast Cancer Subtype Incidence and Distribution by Race/Ethnicity in the United States From 2010 to 2015

Question Are there variations in the incidence of breast cancer subtypes and the distribution of patients across clinicopathological variables associated with race/ethnicity? Findings In this cohort study of 239 211 women with breast cancer, the incidence of HR-negative and ERBB2 (formerly HER2)-positive, HR-positive and ERBB2-positive, and triple-negative breast cancer was higher in Black women compared with non-Hispanic White women. The incidence of histological grade 1 and 2 cancer was lower in Asian/Pacific Islander than non-Hispanic White patients, and a lower incidence of infiltrating duct carcinoma, lobular carcinoma, and tubular adenocarcinoma was seen in Hispanic White vs non-Hispanic White women. Meaning Results of this study suggest that combining epidemiologic data with genomic and molecular profiling data may serve as a future research direction and help in closing the gap in breast cancer subtype incidences and distributions associated with race/ethnicity. Importance Breast cancer is the most commonly diagnosed cancer and the leading cause of death in women worldwide. Yet the racial/ethnic disparity in incidences and distributions of breast cancer remains largely unknown. Objective To examine the racial/ethnic patterns associated with the incidence of the subtypes of breast cancer and distribution of patients across clinicopathological variables. Design, Setting, and Participants This population-based cohort study analyzed data from the Surveillance, Epidemiology, and End Results (SEER) database, which collected data from 18 SEER cancer registries that identified patients with breast cancer in the US diagnosed between January 1, 2010, and December 31, 2015. The inclusion criteria were (1) female patients with primary unilateral breast cancer who underwent surgical treatment; (2) record of estrogen receptor, progesterone receptor, and ERBB2 status; (3) record of medical history and histological subtype of the specified tumor location; and (4) data on patient race/ethnicity, lateral tumor position, tumor size, tumor TNM stage, and number of tumors. Incidence and distribution rates were identified and compared for different molecular subtypes, histological grades, pathological patterns, T stages, TNM stages, and tumor sites of breast cancers for each racial/ethnic group. Patient race/ethnicity was classified as follows: non-Hispanic White, Hispanic White, Black, Asian/Pacific Islander, American Indian/Alaskan Native, and unknown. Data were analyzed from January 1, 2010, to December 31, 2015. Main Outcomes and Measures Incidence rates of 4 molecular subtypes: hormone receptor (HR)-positive and ERBB2-negative, HR-positive and ERBB2-positive, HR-negative and ERBB2-positive, and triple-negative breast cancer (TNBC). Data on distribution by histological grades (grades 1-4 and unknown), pathological patterns, T stages, TNM stages, and tumor sites was also extracted. Annual age-standardized incidence rates and incidence rate ratios (IRRs) were calculated with 95% CIs. Race/ethnicity case-to-case odds ratios were estimated using polytomous regression. Results A total of 239 211 women with breast cancer were analyzed (median [interquartile range]) age, 60 [50-69] years). The annual incidence rate of all breast cancers was 31.3 (95% CI, 31.2- 31.5) per 100 000 people in non-Hispanic White women (the reference group), which was higher compared with the incidence among Black women (IRR, 1.04; 95% CI, 1.02-1.05; P < .001). The incidence rates were also lower in Asian/Pacific Islander (IRR, 0.90; 95% CI, 0.89-0.92; P < .001), American Indian/Alaskan native (IRR, 0.82; 95% CI, 0.81-0.83; P < .001), and Hispanic White women (IRR, 0.79; 95% CI, 0.75-0.83; P < .001). In Black patients, the incidences of the HR-positive and ERBB2-positive (IRR, 1.12; 95% CI, 1.08-1.16; P < .001), HR-negative and ERBB2-positive (IRR, 1.46; 95% CI, 1.38-1.54; P < .001), and TNBC (IRR, 2.07; 95% CI, 2.01-2.14; P < .001) subtypes were higher than those in non-Hispanic White patients, but the incidence of the HR-positive and ERBB2-negative subtype in Black women was lower (IRR, 0.86; 95% CI, 0.84-0.87; P < .001). The incidences of histological grade 1 (IRR, 0.75; 95% CI, 0.73-0.78; P < .001) and grade 2 (IRR, 0.91; 95% CI, 0.89-0.93; P < .001) were lower in Asian/Pacific Islander vs non-Hispanic White patients. Non-Hispanic White patients had a higher proportion of lobular carcinoma (9. 7% [n = 15 718]) and tubular adenocarcinoma (0.6% [n = 997]) than Black (7.2% [n = 1933]; 0.3% [n = 81]), Asian/Pacific Islander (5.7% [n = 1202]; 0.3% [n = 55]), Hispanic White (7.2% [n = 1985]; 0.3% [n = 88]), and American Indian/Alaskan Native patients (7.2% [n = 101]; 0.4% [n = 5]). Conclusions and Relevance This cohort study found notable disparities in incidences and proportions of different molecular subtypes, histological grades, pathological patterns, T stages, TNM stages, and tumor sites associated with race/ethnicity. The findings suggest that combining epidemiologic with genomic and molecular profiling data warrants further research. This cohort study describes the incidence rates of 4 breast cancer molecular subtypes stratified by race/ethnicity among women in the US.