Poorly Differentiated Carcinoma with only Clear Glandular Differentiation Arising from the Bladder Trigone: A Case of Adenocarcinoma or Urothelial Carcinoma?

Invasive urothelial carcinoma (UC) has diverse morphological presentations. Here, we describe the case of a Japanese woman aged in her early 60s with UC with unclear differentiation. The patient presented with distinct glandular differentiation and concurrent cystitis glandularis (CG) and intestinal metaplasia (IM) without a conventional UC component. Up to 2% of patients with bladder cancer develop adenocarcinoma. However, differentiating UC with glandular differentiation (UCg) from adenocarcinoma can be challenging. Although CG and IM are associated with adenocarcinoma, their presence does not necessarily imply that the comorbid cancer is adenocarcinoma. In this case, cytokeratin 7 (CK7) and CK5/6 positivity was assessed to establish the diagnosis of poorly differentiated UCg. A poorly differentiated pure UCg without conventional UC components has not yet been reported, which makes diagnosis extremely difficult. Moreover, because of the highly differentiated glandular structures within poorly differentiated UCs, the mechanism of tumorigenesis remains unclear. Further studies involving a larger case series should be conducted to elucidate the association between CG and IM and investigate the genetic background of these tumors, all of which would improve the accuracy of differentiation between poorly differentiated UC and adenocarcinoma.