Morphological features and mucin expression profile of breast carcinomas with signet-ring cell differentiation.

Signet-ring cells are relatively common in breast cancers but are frequently overlooked. Although previously defined as a subtype of mucin producing carcinomas, breast carcinomas with signet-ring cell (SRC) differentiation nowadays are not considered a distinct entity. The objective of the present study was to characterize the morphological features and mucin expression profile of breast carcinomas with SRC differentiation. All breast carcinomas diagnosed at Centro Hospitalar S. Joao between 1996 and 2006 in which the pathology report mentioned the presence of SRCs (n=11) and four mucinous carcinomas were included in the study. The frequency of SRCs and immunohistochemistry expression of MUC1/MUC2/MUC5AC/MUC6 were evaluated. We confirmed that SRC differentiation can occur in different histological types, including ductal, lobular, mucinous and metaplastic carcinomas. The proportion of SRCs was highly variable (range: 8-70%). Tumors encompassed SRCs of intracytoplasmic lumina and goblet-cell type. A higher percentage of SRCs was associated with lymphovascular invasion (p=0.047). All tumors expressed cytoplasmic and membranous MUC1. Secretory mucins were more frequent in mucinous carcinomas and in carcinomas with extensive SRC differentiation. We conclude that besides the usefulness of mucin immunodetection for the differential diagnosis of carcinomas with SRC differentiation of breast origin, it is important to report SRC differentiation regardless of histological type because of its intrinsic prognostic value.