Clinical outcome and therapeutic impact on neuroendocrine neoplasms of the breast: a national cancer database study

Purpose: Neuroendocrine neoplasms (NENs) of the breast are rare and not well-studied. NEN are subcategorized as well-differentiated neuroendocrine tumor (NET) and poorly differentiated neuroendocrine carcinoma (NEC). The objectives of the current study were to review the clinicopathologic features of NENs, therapeutic efficacy of current systemic therapy and clinical outcomes of NEN of the breast. Methods: Between 2004 and 2015, 420 NET, 205 NEC, 146 Adenocarcinoma with NE differentiation (ACNED) and 1,479,520 of invasive carcinoma, not otherwise specified (IC-NOS) of the breast were identified in the National Caner Database. Overall survival was compared among groups using Kaplan–Meier method and Log-rank test. Multivariate analyses were performed to identify prognostic factors. Results: After adjusting for other prognostic factors, both NET and NEC of the breast showed significantly worse OS than IC-NOS (HR (95% CI) = 1.41 (1.17, 1.72), p = 0.005 and HR (95% CI) = 2.11 (1.67, 2.67), p < 0.001, respectively). Both NET and NEC benefited from endocrine therapy if the tumors were hormonal receptor positive (median OS for treated with vs without: 125 vs 57 months in NET, not reached vs 29 months in NEC). NEC also benefited from chemotherapy (median OS for treated with vs without: 42 vs 34 months), but not NET. Conclusion: NEN is a unique pathologic and clinical entity, which has worse clinical outcome compared to IC-NOS of the breast. Current therapeutics used in the treatment of IC-NOS improve, but do not fully mitigate, the poorer prognosis of NEN patients. More effective therapy for patients with this unique tumor type are needed.