Signet ring variant of lobular carcinoma of the breast: a clinicopathologic and immunohistochemical study.

Signet ring carcinoma of the breast often metastasizes to gastrointestinal tract and female genital tract. We report clinicopathologic features of 10 breast carcinomas with signet ring features, five of which had unusual metastatic patterns. The primary breast tumor in all these cases was lobular carcinoma. Although signet ring cells were prominent in metastatic sites, the primary tumor lacked signet ring cells in two cases. A linitis plastica-like presentation and presence of signet ring cells in gastric metastases raised a strong possibility of primary gastric carcinoma in three cases. The monoclonal antibody to gross cystic disease fluid protein (GCDFP-15) was positive in signet ring cell-rich areas in the primary breast tumor (8/10) and/or in the metastases in all cases. For comparison we studied GCDFP-15 immunoreactivity in 10 infiltrating lobular and 10 infiltrating ductal breast carcinomas with no obvious signet ring cells, and in 14 signet ring carcinomas from other sites (10 gastric, 2 prostatic, 2 colonic). The gastric, colonic, and one prostatic signet ring carcinoma were nonreactive. One prostatic signet ring carcinoma exhibited focal but unequivocal positivity with GCDFP-15. The cases of this report reinforce the concept that signet ring carcinoma of the breast is usually a variant of lobular carcinoma and not a distinct entity. Signet ring cell predominance in metastases, even in the absence of signet ring cells in the primary tumor, attest to the morpho-functional heterogeneity of lobular carcinoma. GCDFP-15 is a sensitive marker for signet ring breast carcinoma and a very useful adjunct tool in the diagnosis of metastatic signet ring carcinoma of mammary origin.