Invasive Duct Carcinoma of the Breast With Dominant Signet-Ring Cell Differentiation: A Microsatellite Stable Tumor With Aggressive Behavior.

Abstract

Invasive duct carcinoma, no special type (IDC, NST), of the breast with signet-ring cell differentiation is uncommon. This study was undertaken to describe the clinicopathologic characteristics of IDC, NST, with dominant signet-ring cell differentiation, and look for microsatellite instability in these tumors. Cases of IDC, NST, with dominant signet-ring cell differentiation, diagnosed over the past 2 years, were retrieved. Detailed clinical and pathologic analyses were performed. Immunohistochemistry was performed for estrogen receptor, progesterone receptors, Her-2 neu, Ki-67, E-cadherin, CK7, and CK20. Microsatellite instability was examined using immunohistochemistry for the 4 mismatch repair proteins: MLH1, MSH2, MSH6, and PMS2. Of the total 1646 cases of IDC, NST, only 5 cases showed dominant signet-ring cells (ranging from 70% to 100%) and strong E-cadherin positivity and were diagnosed as IDC, NST, with dominant signet-ring cell differentiation. The age ranged from 32 to 65 years. Two cases were of histologic grade 3 and the remaining cases were grade 2 tumors. Four patients had T2 tumor and 1 had T3 tumor. All cases had axillary lymph node metastasis and distant metastasis was present in 1 case. All cases were microsatellite stable. Signet-ring cell differentiation in IDC, NST, is rare and associated with a high histologic grade. Lymph node metastasis and distant metastasis are common, indicating an aggressive clinical behavior. Thus, they should be recognized separately as they may warrant aggressive management. However, these are microsatellite-stable tumors in contrast to signet-ring cell tumors of other organs.