The changing phenotypic appearance of a malignant vulval neoplasm containing both carcinomatous and sarcomatous elements.

We describe the changing phenotypic appearance over a 7-year period of a malignant neoplasm of the vulva. This lesion was studied by light and electronmicroscopy and immunohistochemical techniques. The tumour contained both carcinomatous and sarcomatous elements including osteosarcomatous differentiation. To our knowledge osteosarcomatous differentiation has not been reported previously at this site. We submit that the best term for this type of neoplasm, based on tumour differentiation rather than reputed histogenesis, is carcinosarcoma. Tumours such as these occurring in the female genital tract should be distinguished from metastatic mixed Müllerian tumours.