Stromal osseous metaplasia in carcinoma of the bladder

Osseous metaplasia of the stroma of carcinomas of the bladder is a rare finding that must be distinguished from osteosarcoma and carcinosarcoma. We report a case of multifocal osseous metaplasia in a high grade urothelial carcinoma with extensive glandular differentiation, arising in the base of the bladder of an 84-year-old man. Reports of 11 other cases of stromal osseous metaplasia in primary bladder carcinomas and of 5 cases of stromal osseous metaplasia in metastases of bladder carcinoma are reviewed.