[A case of sarcomatoid carcinoma of the bladder: immunohistochemical study on histogenesis of sarcomatoid elements].

An 82-year-old man with microhematuria and class V cells in his urinary cytologic specimen was referred to our clinic. Cystoscopy revealed a solid, broad-based tumor of 1 cm in diameter in the bladder diverticulum. A partial cystectomy was performed. The tumor was composed of transitional cell carcinoma (TCC), sarcomatous spindle cells and the area of transition between TCC and spindle cells. The histopathological diagnosis was sarcomatoid carcinoma. Immunohistochemical examination showed that the spindle cells and the area of transition were positive for keratin, cytokeratin, vimentin and muscle actin. The histopathological and immunohistochemical transitions between the TCC and the spindle cells suggested that the sarcomatous elements originated from the TCC during tumor progression.