Immunohistochemical Characterization of Signet-Ring Cell Carcinomas of the Stomach, Breast, and Colon

We studied the immunophenotype of signet-ring cell carcinoma (SRCC) of the stomach (30 cases), breast (21 cases), and colon (9 cases) with the following expression patterns: (1) breast: consistent, MUC1 (21 100%), cytokeratin (CK) 7 (20 95%), estrogen receptor (ER; 17 81%); infrequent, E-cadherin (6 29%), MUC2, MUC5AC, CK20 (1 5% each); negative, CDX2 and hepatocyte paraffin 1 (Hep Par 1; 0 0% each); (2) gastric: frequent, CDX2 (27 90%) and Hep Par 1 (25 83%); variable, E-cadherin and CK20 (17 57% each), MUC2 and MUC5AC (15 50% each), MUC1 (5 17%); negative, ER (0 0%); and (3) colon: frequent, MUC2 (9 100%), CDX2 and MUC5AC (8 89% each); infrequent or negative, MUC1 (3 33%), Hep Par 1 (2 22%), ER (0 0%). Immunohistochemical staining distinguished breast from gastric SRCC (ER, MUC1, Hep Par 1, CDX2) and colon SRCC (ER, CDX2, MUC2, and MUC5AC). Gastric and colon SRCCs showed a similar staining pattern for antibodies tested except for Hep Par 1 and CDX2 (gastric, 83% Hep Par 1 positivity and heterogeneous, weak, patchy CDX2 nuclear staining; colon, 22% Hep Par 1 positivity and homogeneous, strong, diffuse CDX2 nuclear staining). About half of the cases of gastric SRCC expressed MUC2 and MUC5AC, whereas virtually all cases of colon SRCC expressed them.