Sex-stratified outcomes, hormone receptor expression, and treatment utilization in neuroendocrine carcinoma of the breast: A population-based analysis.

Abstract

e12757 Background: Neuroendocrine carcinoma of the breast (NECB) is a rare malignancy with limited contemporary population-level data describing sex-stratified clinicopathologic features, treatment utilization, and survival outcomes. Given the rarity of NECB in men, descriptive population-based benchmarks are needed to contextualize outcomes in this understudied subgroup. Methods: We performed a retrospective population-based analysis of patients diagnosed with NECB using SEER Research Plus. Demographics, treatment utilization (surgery and chemotherapy), and hormone receptor expression were summarized by sex. Progesterone receptor (PR) status was evaluated due to greater completeness relative to other receptor variables in earlier diagnosis years. Observed overall survival was summarized descriptively by sex overall and stratified by receipt of surgery and chemotherapy, with survival estimates reported at 12 to 60 months. Given the rarity of NECB in men, analyses were descriptive and hypothesis-generating, and no formal comparative modeling was performed. Results: A total of 398 patients with NECB were included in the survival cohort, of whom 396 (99.5%) were female and 2 (0.5%) were male. In the PR-annotated subset (n = 350), 345 patients were female and 5 were male. PR positivity was observed in 54.2% of female patients (187/345) and 80.0% of male patients (4/5), though estimates among men were limited by small sample size. Among female patients, observed overall survival was 81.5% at 12 months (95% CI, 77.3–85.0) and 56.8% at 60 months (95% CI, 51.5–61.7). Observed overall survival for the combined cohort was 81.6% at 12 months and 57.0% at 60 months. Male patients demonstrated no observed death events during available follow-up; however, confidence intervals were not estimable due to sparse event counts. In analyses stratified by receipt of surgery and chemotherapy, female patients demonstrated expected declines in survival over time, while sex-stratified estimates among men remained limited. Conclusions: In this population-based cohort, NECB in men was exceedingly rare, limiting definitive sex-based outcome comparisons. Sex-stratified descriptive analyses demonstrated a high prevalence of hormone receptor expression and substantial heterogeneity in survival outcomes. These findings are hypothesis-generating and provide population-level descriptive benchmarks, highlighting the need for pooled multi-registry efforts to better characterize sex-specific biology, treatment patterns, and outcomes in NECB.