Abstract P1-08-03: An early look at incidence and survival by HR and HER2 status among young US women with stage I-III breast cancer: SEER 2010-15

Background: Population-based contemporary incidence and survival patterns for breast cancer by receptor status (hormone receptor [HR]; human epidermal growth factor receptor 2 [HER2]) among young US women have not been described. Methods: We identified pre-, peri-, and early postmenopausal women ages 20-29 (n=1,617), 30-39 (n=12,910), 40-49 (n=47,313), and 50-59 (n=68,870) diagnosed with Stage I-III breast cancer from 2010-15 in the Surveillance, Epidemiology and End Results (SEER) database using SEER*Stat version 8.3.5. Of these, respective totals for women with reported HR and non-borderline HER2 status were 1533 (94.8%), 12,225 (94.6%), 44,684 (94.4%), and 64,844 (94.2%). Using this analytic sample, we estimated annual percentage change (APC) in incidence. Restricting the sample to women diagnosed from 2010-14, we estimated four-year survival (maximum available follow-up). Analyses were stratified by age group and receptor status. Results: The proportion of HER2 + /HR + cancer was highest among women 20-29, decreasing with increasing age; that for HER2 + /HR - cancer was lower, differing less across age groups (Table 1). For HER2- cancer, the proportion of HER2 - /HR + cancer was lowest for women 20-29 and increased with age; the opposite pattern was observed for HER2 - /HR - cancer. Overall, stage I-III breast cancer increased in incidence from 2010-15 for all age groups, with the APC greatest in women 20-29 [2.20](30-39 [1.98], 40-49 [1.91], 50-59 [1.62]). The patterns for the APCs by age and receptor status tended to reflect those for the observed proportions, except those for women with HER2 + /HR - cancer, which tended to increase with increasing age (Table 1). Four-year survival estimates for women 20-29, although imprecise, differed by HER2 status, being higher for those with HER2 + than HER2 - cancer, and this difference persisted for HR + and HR - cancers among these women (Table 2). In the other age groups, survival differed by HR status, being higher for women with HR + than HR - cancer. Conclusions: Using SEER data representative of over one-quarter of the US population, Stage I-III breast cancer has increased among young women in recent years. In particular, HER2 + /HR + and HER2 - /HR - cancers were over-represented and estimated to have the highest APCs among women 20-39 compared to those 40-59. Receptor status was observed to influence survival differently across age groups. The differences in four-year survival observed among women 20-29 with HR + cancers may have implications as we consider anti-estrogen therapy options for these youngest premenopausal women. Citation Format: Thomas A, Rhoads A, Pinkerton E, Melin S, Oleson JJ, McNally LR, Hundley WG, Conway K, Lynch CF, Romitti PA. An early look at incidence and survival by HR and HER2 status among young US women with stage I-III breast cancer: SEER 2010-15 [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-08-03.