Validation of prognostic significance of the proposed uniform classification framework in neuroendocrine neoplasms of the breast

Purpose: A uniform classification framework for neuroendocrine neoplasms (NENs) in all the organ systems has been recently proposed by an International Agency for Research on Cancer (IARC) and World Health Organization (WHO) expert panel. Based on the new classification system, the NENs of the breast are divided into well-differentiated neuroendocrine tumors (NETs) and poorly differentiated neuroendocrine carcinomas (NECs). This study is aimed to analysis the prognostic differences between NENs and invasive ductal carcinomas of no special type (IDCs-NST). Methods: The surveillance, epidemiology, and end results (SEER) database released on November 2018 was used for this study. Between 2003 and 2016, 361 NENs (NET = 239, NEC = 122) of the breast and 491,908 of IDCs-NST were identified. Survival analysis was performed for disease-specific survival (DSS) and overall survival (OS). Results: The 5-year DSS of NET, NEC, and IDC-NST was 63.39%, 46.00%, and 89.17%, respectively. And the 5-year OS of NET, NEC, and IDC-NST was 55.66%, 38.87%, and 83.17%, respectively. Within the same clinical stage or grade, NETs and NECs of the breast had worse DSS and OS than corresponding stage or grade IDCs-NST (all P < 0.050). In univariate and multivariate survival analysis, NENs of the breast had significantly worse DSS and OS than IDCs-NST (P < 0.001). Conclusion: The universal classification framework for NEN allowed us to further refine the breast carcinoma with neuroendocrine differentiation as a unique pathologic and clinical entity, which has worse clinical outcome compared to IDC-NST.