LAUSR

572 Background: Breast cancer is the second leading cause of cancer death in U.S. women. On the molecular level, breast cancer is a heterogeneous disease. Heterogeneous expressions of estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2) are etiologically and clinically meaningful, as they map to distinct risk factors and different treatment strategies. Although breast cancer mortality has been declining since 1990, little is known about mortality trends according to molecular subtypes at the population level. Methods: We examined the incidence-based mortality rates and trends among women who were diagnosed with invasive breast cancer from 2010 through 2017 using the Surveillance, Epidemiology, and End Results (SEER) database. We defined incidence-based mortality using a moving 5-year calendar period starting in 2014. We further assessed mortality according to breast cancer molecular subtypes: luminal A (ER and/or PR positive, HER2 negative), luminal B (ER and/or PR positive, HER2 positive), HER2-enriched (HER2 over-expressed or amplified, ER and PR negative) and triple-negative (ER and PR negative, HER2 negative) tumors. We calculated annual percent changes (APC) in incidence-based mortality using joinpoint regression models. Results: Overall, incidence-based mortality for breast cancer significantly decreased by 1.5% annually from 2014 through 2017 (APC, -1.5%; 95% coefficient interval [CI], -2.3% to -0.7%; p<0.001). Incidence-based mortality decreased annually by 2.0% for luminal A breast cancer (APC, -2.0%; 95% CI, -3.7% to -0.3%; p<0.001), 2.1% for luminal B breast cancer (APC, -2.1%; 95% CI, -5.4% to 1.4%; p=0.1), 1.1% for triple-negative breast cancer (TNBC) (APC, -1.1%; 95% CI, -2.1% to -0.0%; p<0.001). However, incidence-based mortality for HER2-enriched breast cancer increased 2.3% annually during the study period (APC, 2.3%; 95% CI, -2.4% to 7.2%; p=0.2). Conclusions: Between 2014 and 2017, incidence-based mortality for luminal A, luminal B, and TNBC decreased among U.S. women, with a larger decrease observed for luminal tumors. However, incidence-based mortality for HER2-enriched breast cancer increased. The favorable incidence-based mortality trends for luminal tumors and TNBC are likely due to the continuing improvement in treatments and early detection. The increasing trend of incidence-based mortality for HER2-enriched breast cancer constitutes a priority for cancer control activities and further research.