Neuroendocrine differentiation in breast carcinoma: clinicopathological features and outcome

Aims Primary neuroendocrine (NE) breast carcinoma (BC) is an entity with a wide range of prevalence and poorly defined clinical behaviour. We evaluated the prevalence, clinicopathological features and clinical outcome of NEBC. Methods and results Immunohistochemical staining for synaptophysin and chromogranin A was performed on whole sections from 1232 consecutive cases of invasive BC. We divided NEBC into focal (10–49% positive cells) and diffuse (≥50% positive cells) and compared the outcome of patients with NEBC with strictly matched non‐NEBC. A total of 128 BC showed NE differentiation (10.4%): 84 diffuse (6.8%) and 44 focal (3.6%). NE differentiation showed a significant association with T4 stage (P = 0.001), solid‐papillary and mucinous histotype (P