Immunohistochemical and ultrastructural characterization of the signet-ring cell carcinoma component in a case of urothelial carcinoma of the urinary bladder.

Characterization of the signet-ring cell carcinoma (sig) component of a urothelial carcinoma (UC) in the urinary bladder of a 64-year-old man, obtained by transurethral resection of bladder tumor (TUR-BT), is reported. In the present case, a characteristic sig component was detected in approximately 20% of UC, G2 tissues. The sig cells were morphologically similar to those found in gastric cancers and were positively stained with periodic acid-Schiff reaction and Alcian blue and mucicarmine stains. Immunohistochemically, the sig cells were selectively positive for carcinoembryonic antigen (CEA), MUC2, and MUC5AC. These immunohistochemical characteristics were similar to those of sig cells in the stomach, except for the positivity with MUC2. It is interesting to note that CAM5.2-positive sig cells were surrounded by CAM5.2-positive UC cells in a solid nest with no apparent associated adenocarcinoma element. In addition, the ultrastructure of sig cells showed multivacuolar cytoplasmic mucin, which proved to be similar to the ultrastructure of gastric cancers. In the present case of UC, G2 was associated with a sig component. Regarding the origin of the sig component in the bladder, it has been suggested that MUC2-positive sig cells in the bladder might be derived directly from metaplasia of UC, without an associated adenocarcinoma component. From this perspective, it may be noteworthy that sig cells in the bladder were selectively positive for MUC2, exhibiting common antigenicity with mucous cells of the gastric intestinal metaplasia. Because UC associated with a sig component carries a worse prognosis than ordinary UC, the presence of the sig component in any UC should be evaluated even within TUR-BT tissues, as in the present case.