Cytomorphological features of sebaceous carcinoma of the breast.

Sebaceous carcinoma of the breast is an extremely rare histological subtype of breast cancer, with fewer than 30 cases reported to date. Because of its extremely rare histological presentation, there are few case reports that highlight its cytological findings. In this case report, the cytomorphological features of a sebaceous carcinoma of the breast are described in detail. Cytomorphological analysis revealed atypical cells presenting predominantly as loose clusters. No tubular or papillary structures were evident in the clusters and no mucin production was observed. The diagnosis of sebaceous carcinoma of the breast requires prominent sebaceous differentiation of cells. In Papanicolaou-stained smears, the differentiated tumor cells were found within the yellowish clusters. When these yellowish clusters were observed at high magnification and shifted out of focus, the sebaceous differentiation of tumor cells could be recognized. This finding is an advantage of observing Papanicolaou-stained specimens. Like previous reports, some individual cells showing sebaceous differentiation were also observed. In cases where many yellowish clusters appear, close observation of the interior of the clusters can confirm the presence of sebaceous differentiation of tumor cells and serve as a diagnostic clue for the cytological diagnosis of sebaceous carcinoma of the breast.