Neuroendocrine neoplasms of the breast: a multicenter retrospective Italian study

The aim of our retrospective study was to describe the immunophenotypic characteristics of neuroendocrine breast neoplasm (BNEN), a peculiar and rare type of breast carcinoma.

Pathological data from 51 patients affected by BNEN were retrospectively evaluated, and 44 patients were considered eligible (7 patients with incomplete data were excluded). The patients were followed in six different Italian hospitals between 2009 and 2019. The histological samples, collected by biopsies and/or surgery pieces, were analyzed to determine: 1) tumor histology; 2) immunophenotypic pattern; 3) presence of lymphatic infiltration; 4) presence of necrosis.

The median age of the patients included in our analysis was 70 years (67.6±13.7 years). As concerns the histological type we identified 7 cases of well-differentiated neuroendocrine carcinomas (16%), 8 cases of poorly differentiated/small cell neuroendocrine carcinoma (18%), 29 cases of breast carcinomas with neuroendocrine differentiation (66%). From the analysis of breast-specific immunophenotype we identified: 24 cases (54%) of Luminal A pattern; 9 cases (20%) of Luminal B pattern; 8 case (18%) of triple negative pattern. The presence of lymphatic infiltration was assessed in 29 samples and it was observed in 13 cases (45%), necrosis was assessed in 29 samples and was absent in 72% of all cases (21 samples). Neuroendocrine markers expression was heterogeneous with a prevalence of synaptophysin (positivity in 95%); chromogranin A was evaluated in 31 samples and it was positive in 58% of cases.

in our series BNENs mainly affect a post-menopausal population and luminal A pattern is the most frequent immunophenotype. As expected, lymphatic infiltration is most frequently reported in invasive breast cancer with neuroendocrine differentiation; necrosis is absent in well-differentiated neuroendocrine carcinomas. Synaptophysin and chromogranin A are important markers for the diagnosis of BNEN.