OBJECTIVETo study the clinical features and histopathology of the neuroendocrine carcinoma (NEC) of the breast.

METHODSTwenty-two cases of NEC of the breast were analysed by morphology and immunohistochemistry using synaptophysin, chromogranin A, NSE, CD56, estrogen receptor (ER), progesterone receptor (PR), HER2, EGFR, CK5/6, CK14, p63, E-cadherin, p120, p53 and Ki-67 staining. HER2 gene amplification was detected by fluorescence in situ hybridization (FISH) for cases with HER2 protein expression 2+. The diagnosis of breast NEC relies on the expression of neuroendocrine markers expression in more than 50% of tumor cells, and no evidence of neuroendocrine carcinoma in any other parts of the body at the same time.

RESULTSThe patients aged from 31 to 96 years (mean 65.2 years), and all were female but one. Amongst the 22 patients studied, the NECs were in the left breast in 15 cases (68.2%) and in the right breast in seven cases (31.8%); the tumor size was 0.5 to 5.5 cm (mean 2.7 cm). Lymph node metastasis was found in six cases. Basing on the morphologic features, these 22 cases were categorized into six subtypes including nine cases of solid cohesive, six of mucinous, three of solid papillary, two of small cell, one of large cell and one of alveolar variants. Immunohistochemically, the expression rate of markers was 100% (22/22) for synaptophysin, 12/13 for NSE, 54.5% (12/22) for chromogranin A, and 5/16 for CD56. Also, 90.5% (19 of 21) of cases expressed ER, 81.0% (17 of 21) of cases expressed PR, and none expressed EGFR, CK5/6, CK14 and p63. HER2 protein over-expression (3+) and gene amplification was not detected in any case. All cases (19/19) were positive for membrane staining for E-cadherin and p120. p53 expression was seen in 6 of 17 cases. Ki-67 labeling index was less than 3% in 9.5% (2/21) of the cases, 3% to 20% in 66.7% (14/21) of the cases and more than 20% in 23.8% (5/21) of the cases. Both cases of HER2 (2+) did not show gene amplification by FISH. On the basis of immunophenotypes, most of the breast NECs were of the luminal molecular subtype, but not HER2-overexpression or basal-like subtypes.

CONCLUSIONSNEC of breast more likely occurs in elderly patients and in the left breast than the right breast. The most common morphology is the solid cohesive subtype, followed by the mucinous variant.