Breast cancer in Asian Americans in California, 1988-2013: increasing incidence trends and recent data on breast cancer subtypes.

PURPOSE: In contrast to other US racial/ethnic groups, Asian Americans (AA) have experienced steadily increasing breast cancer rates in recent decades. To better understand potential contributors to this increase, we examined incidence trends by age and stage among women from seven AA ethnic groups in California from 1988 to 2013, and incidence patterns by subtype and age at diagnosis for the years 2009 through 2013.

METHODS: Joinpoint regression was applied to California Cancer Registry data to calculate annual percentage change (APC) for incidence trends. Incidence rate ratios were used to compare rates for AA ethnic groups relative to non-Hispanic whites (NHW).

RESULTS: All AA groups except Japanese experienced incidence increases, with the largest among Koreans in 1988-2006 (APC 4.7, 95% CI 3.8, 5.7) and Southeast Asians in 1988-2013 (APC 2.5, 95% CI 0.8, 4.2). Among women younger than age 50, large increases occurred for Vietnamese and other Southeast Asians; among women over age 50, increasing trends occurred in all AA ethnic groups. Rates increased for distant-stage disease among Filipinas (2.2% per year, 95% CI 0.4, 3.9). Compared to NHW, Filipinas and older Vietnamese had higher incidence rates of some HER2+ subtypes.

CONCLUSIONS: Breast cancer incidence rates have risen rapidly among California AA, with the greatest increases in Koreans and Southeast Asians. Culturally tailored efforts to increase awareness of and attention to breast cancer risk factors are needed. Given the relatively higher rates of HER2-overexpressing subtypes in some AA ethnicities, research including these groups and their potentially unique exposures may help elucidate disease etiology.