Mucinous carcinoma of the breast: a comparative study on cytohistological findings associated with neuroendocrine differentiation

Objective Mucinous carcinoma (MCA) may show neuroendocrine differentiation (ND), but the cytological features characteristic of ND remains elusive. We compared fine needle aspiration (FNA) findings of MCA between cases with high and low degrees of ND. Methods Histological sections of 37 MCA cases were immunohistochemically evaluated for expression of chromogranin A and synaptophysin, and were graded as 0 to 3+ degrees of ND. They were divided into low ND (grade 0 and 1+) and high ND (grade 2+ and 3+) groups. Pre‐operative FNA samples of each group were assessed for cytological features. Results The mean age of the high ND group (n = 18) was higher than the low ND group (n = 19, P = 0.01). In FNA samples of the high ND group, 17 cases showed moderate to severe degrees of discohesiveness, but low ND cases mainly showed no or only mild discohesiveness (P < 0.001). Nine of the low ND cases displayed overlapped, cohesive cell clusters, whereas, in the high ND cases, the cells were arranged in a loose, flat and monolayered pattern (P = 0.045). Fourteen of the high ND cases had round nuclei, but oval nuclei were predominant in the low ND cases (P = 0.027). The nuclei were eccentrically located in 12 of the high ND cases but were centrally located in 14 of the low ND cases (P = 0.01). Conclusions Mucinous carcinoma with high ND may be diagnosed by the presence of discohesiveness, a flat, monolayered pattern, and round or eccentrically located nuclei. Features of ND in carcinomas in other organs, such as intracytoplasmic granules and coarse chromatin, may not be reliable cytological features of ND in MCA. This study describes the detailed cytological features of the Mucinous carcinoma (MCA) of breast with neuroendocrine differentiation (ND) in 37 patients. The staining distribution of ND markers was semi‐quantitatively graded as high and low ND groups. This was correlated with the clinical profile of these patients.