e12758 Background: Neuroendocrine carcinoma of the breast (NECB) is a rare malignancy accounting for < 0.5% of breast cancers, with limited contemporary population-level data describing outcomes. Prior studies were constrained by small sample sizes, heterogeneous histologic definitions, and earlier treatment eras. We performed a population-based analysis using the SEER 21 Registries database to characterize clinicopathologic features, treatment utilization, and overall survival (OS) in NECB. Methods: We conducted a retrospective cohort study of patients diagnosed with NECB between 2000 and 2021 using Surveillance, Epidemiology, and End Results (SEER) 21 Registries, Research Plus database (N = 901). NECB was identified using predefined ICD-O-3 histology codes for neuroendocrine neoplasms of the breast. Demographics, race/ethnicity, Combined Summary Stage (2004+), and receipt of surgery, radiation, and chemotherapy were summarized descriptively. Given low individual frequencies, histologic subtypes were analyzed collectively. OS was estimated using Kaplan–Meier methods overall and stratified by stage at diagnosis. Analyses of hormone receptor subtype were restricted to cases diagnosed in 2010–2021, reflecting availability of contemporary biomarker data. Results: Among 901 patients, 98.3% were female. Race/ethnicity distribution was 69.7% non-Hispanic White, 13.0% Hispanic, 12.4% non-Hispanic Black, 4.6% non-Hispanic Asian/Pacific Islander, and 0.3% non-Hispanic American Indian/Alaska Native. Among staged cases (n = 760), disease was localized in 47.1%, regional in 26.1%, distant in 22.8%, and in situ in 4.1%. Treatment included surgery in 64.8%, radiation in 56.6%, and chemotherapy in 32.1%. Overall, 53.5% experienced death events. Median OS for the cohort was 9.0 years, with 5- and 10-year OS rates of 59.5% and 45.2%, respectively. Stage-stratified median OS was 15.0 years for localized disease, 8.0 years for regional disease, and 2.0 years for distant disease, with corresponding 5-year OS rates of 74.3%, 61.4%, and 22.2%. Among cases diagnosed in 2010 or later with available subtype data (n = 360), tumors were predominantly hormone receptor–positive/HER2-negative (74.2%), followed by triple-negative disease (22.2%). Conclusions: In this large SEER 21 Registries cohort, NECB demonstrated substantial mortality with survival strongly dependent on stage at diagnosis. Despite multimodality treatment, advanced-stage disease remained associated with poor outcomes. These findings provide contemporary national survival benchmarks for NECB and highlight the need for NECB-specific clinical investigation and risk-stratified therapeutic strategies.
Shah et al. (Thu,) studied this question.