Mucin Profiles in Signet-ring Cell Carcinoma

Context.—Signet-ring cell carcinoma (SRCC) is a poorly differentiated mucin-producing adenocarcinoma that may arise from many different organs, but all SRCCs share identical morphology. It is not possible to differentiate sites of origin for metastatic SRCC based on morphology alone. Mucins are high-molecular-weight glycoproteins differentially expressed in glandular epithelia and in adenocarcinomas. Objective.—To identify mucin profiles of primary and metastatic SRCCs using immunohistochemistry to determine whether mucin staining could help distinguish sites of origin. Design.—Forty-seven SRCCs, including 38 primary (21 stomach, 11 colorectum, and 6 breast) and 9 metastases from these primary sites were retrieved from archival files. Consecutive tissue sections were immunostained with monoclonal antibodies against MUC1, MUC2, MUC4, MUC5AC (MUC5), and MUC6 on separate slides. Cytoplasmic staining was scored based on proportion of positive tumor cells as follows: 0+ (<5%), 1+ (5%–25%), 2+ (26%–50%), and 3+ (>50%). Mucin profiles were recorded as MUC+, MUCv, and MUC− for consistent, variable, and negative expression, respectively. Results.—The mucin profiles for gastric, colorectum, and breast SRCCs are MUC1·2·4·5·6v, MUC2·4+/MUC5v/ MUC1·6−, and MUC1+/MUC2·5·6v/MUC4−, respectively. Mucin profiles of metastatic cases shared profiles with their respective primaries. Conclusions.—Signet-ring cell carcinomas of the stomach, colorectum, and breast have distinct mucin expression patterns that are maintained in metastases. Mucin profiling may be useful to identify the origin of a metastatic SRCC of unknown primary.