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Objective: To study the clinicopathologic features of pure mucinous carcinomas of the breast with diffuse micropapillary pattern., Methods: Twenty-six cases of micropapillary variant of pure mucinous carcinoma of the breast were retrospectively reviewed by light microscopy, immunohistochemistry and clinical data analyses., Results: The age of 26 female patients ranged from 30 to 77 years old, of which 12 cases with clinical details available were mean 54 years old. The tumor diameter ranged from 0.8 to 9.0 cm (mean 3.2 cm). Ipsilateral axillary nodal metastases were identified in 3 cases. Cutaneous involvement was also found in 2 cases. The tumor cells showed the similar architectural arrangement as in invasive micropapillary carcinoma, with peripheral borders of the cell clusters highlighted by epithelial membrane antigen. Various amount of mucin occupied the retraction spaces around the tumor cells. Compared with conventional pure mucinous carcinoma of the breast, mucinous carcinomas with micropapillary pattern showed different nuclear grades (19 cases of grade I, 2 cases of grade II, 5 cases of grade III). The micropapillary cell clusters varied in size (22 cases of big micropapillary and 4 cases of small). Intraductal carcinoma was observed in 12 cases. Calcification and psammoma bodies were observed in 8 cases. Immunophenotyping, the tumor cells were with higher expression of hormone receptors, but HER2 were negative. Ki-67 positive index was 1% ∼ 70%. Neuroendocrine differentiation was observed in 6 cases., Conclusions: The micropapillary variant of pure mucinous carcinoma of the breast, which mainly occurs in younger women, may carry the similar propensity for angioinvasion and nodal metastasis as infiltrating micropapillary carcinoma at least in cases with high nuclear grade. This morphologic subtype needs to be distinguished from conventional pure mucinous carcinoma of the breast and treated properly.

Objective: To study the clinical features and histopathology of the neuroendocrine carcinoma (NEC) of the breast., Methods: Twenty-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., Results: The 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., Conclusions: NEC 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.