Organ-confined plasmacytoid urothelial carcinoma: implication of the lack of expression of the receptor tyrosine kinase MET

Plasmacytoid urothelial carcinoma (PUC), a morphological variant of urothelial carcinoma (UC), is composed of cancer cells that resemble plasma cells, monocytes, or both, and is clinicopathologically distinguished by its aggressive, non-organ-confined features. Here, we present a case of a patient with PUC with early invasion at diagnostic transurethral resection. Histopathologically, no residual cancer or lymph node metastasis was observed by total cystectomy. The patient remains disease-free after 18 months, without undergoing adjuvant chemotherapy. Interestingly, the immunoreactivity of MET, a receptor tyrosine kinase expressed in many invasive UCs, was minimal in the cancer cells. In contrast, archival pathological, non-organ-confined PUC cells exhibited strong MET immunoreactivity. The present case may imply a role for the MET protein in the aggressive behavior of PUCs. We propose the putative usefulness of MET inhibitors for the treatment of aggressive PUCs.