While there is no established mechanism for osseous metaplasia in any type of carcinoma in feline patients, mucin, osteopontin, MAPK, P53, and CD44 produced by tumor cells are thought to be involved in osseous metaplasia in human intestinal carcinoma (23, 24) and bone morphogenetic proteins (BMP) induced transformation of stromal cells into osteoblasts, alkaline-phosphatase activity, local calcium and phosphate levels are thought to be involved in osseous metaplasia in human urothelial carcinoma (18). The gene discussed is SPP1; the disease is urothelial carcinoma.