Answer: Metastatic adenocarcinoma

Histology: In areas the tumor has a papillary pattern where the papillae are lined by cells with abundant eosinophilic cytoplasm, some containing mucin vacuoles. Present in the underlying stroma is a proliferation of tubules that have similar cytoplasm yet appear extremely cytologically benign. Occasionally, some of the nuclei have a little bit more atypia with enlarged nuclei and visible nucleoli. In areas, one can appreciate the mucinous appearing glands are undermining normal appearing urothelium and are situated within the lamina propria.

Discussion: The key to recognizing secondary involvement of the bladder by other tumors is the presence of tumor undermining normal urothelium. This is typical for adenocarcinoma of the prostate when it invades the bladder as well as for other tumors. Secondary tumors involving the bladder are rare with some of the more common tumors being melanoma, breast, stomach, lung and kidney. Rare examples of other sites metastatic to the bladder include pancreas as in the current case, testis, gallbladder, liver, uterus, skin, appendix and tongue. These tumors are distinct from those secondarily involving the bladder by contiguous spread which is seen with adenocarcinomas of the colon, uterine cervical squamous carcinoma, and adenocarcinoma of the prostate. DPC4 is lost in about 50% of pancreas cancers and a smaller percentage of gastric carcinomas. In other tumors, DPC4 is retained with it being present in the stroma, hematopoietic cells, as well as the tumor. In the current case, the absence of nuclear staining within the nuclei of the mucinous glands as contrasted to the positivity of DPC4 in the stromal nuclei is evidence of its loss, and along with the histology virtually diagnostic of metastatic adenocarcinoma from the pancreas. Following diagnosis, the patient was worked up and noted to have a pancreas mass.