Recent trends in breast cancer incidence among 6 Asian groups in the Greater Bay Area of Northern California.

Asians and Pacific Islanders are typically aggregated in United States (US) cancer statistics even though the few studies that have considered subgroups separately have found marked differences in cancer incidence. The objective of this study was to evaluate trends in breast cancer incidence rates separately for US Chinese, Japanese, Filipino, Korean, South Asian and Vietnamese women overall and by age at diagnosis, histologic subtype and stage at diagnosis. Age-adjusted incidence rates and annual percent changes (APC) of new, primary breast cancer diagnosed in the Greater Bay Area Cancer Registry of Northern California (1990-2002) were calculated using SEER*Stat. In women under 50 years of age, annual incidence rates decreased for Japanese (APC = -4.1, p = 0.02) and Filipinas (APC = -1.9, p = 0.11), and increased or fluctuated in other subgroups over the study period. In women 50 years or older, rates of invasive breast cancer increased for most subgroups, except Filipinas (APC = -1.3, p = 0.32), and in Japanese until 1998-2000. Rates of breast cancer in situ increased in most subgroups from 1990 to 2002, as did rates of lobular breast cancer for Chinese (APC = +7.46, p < 0.01) women. In Japanese women, rates of lobular breast cancer were highest in 1995-1997 and decreased thereafter. Our data support the notion that the prevalence of established risk factors influence breast cancer incidence, as breast cancer rates increased for more recently immigrated groups and decreased among more established groups, and may suggest leads into other avenues of research, such as genetic differences, that may explain differences in incidence rates among Asian subgroups.