POU2F3-positive small cell carcinoma of the bladder: A clinicopathologic analysis of 4 cases and literature review.

ABSTRACT

POU class 2 homeobox 3 (POU2F3)-positive small cell bladder carcinoma (SCBC) is an extremely rare entity, and its clinicopathologic features have not been fully described. Here, we investigated the clinicopathologic features of 4 cases of POU2F3-positive small cell bladder carcinoma (SCBC) and reviewed the literature. We collected 12 cases of SCBC from our departmental archives and detected the expression of POU2F3 by immunohistochemical (IHC) staining. Selected cases with or without POU2F3 expression were subjected to gene expression analysis between two different groups using DESeq2 software. We identified 4 POU2F3-positive SCBC patients, 2 males and 2 females, with a mean age of 77 years. Three patients had hematuria, and 1 patient had dysuria. Radiologic findings showed a bladder mass. Pathologic diagnosis showed that 3 cases were pure SCBC and 1 was mixed urothelial cancer (UC). Histopathologically, four POU2F3-positive SCBC tumors were composed of small round cells with sparse cytoplasm, the nuclei were salt-and-pepper-like or finely granular. Tumor cells showed characteristic cytoplasmic staining with punctate positive signals for cytokeratin. Syn and CD56 were diffusely positive in all the 4 patients. CgA was positive in only one patient. POU2F3-positive SCBC showed higher expression levels of POU2F3, HMGA2 and PLCG2 genes by RNA-Seq. Our data showed the specific clinicopathologic features of 4 rare POU2F3-positive SCBC cases, and the distinct molecular feature was observed between POU2F3-positive and negative SCBC in the limited number of cases.