Testicular sex cord stromal tumour with granulosa cell differentiation: detection of steroid hormone receptors as a possible basis for tumour development and therapeutic management. A testicular sex cord stromal tumour with granulosa cell differentiation, typical of granulosa cell tumours of the adult type, was investigated immunohistologically on snap frozen and paraffin wax embedded material. The predominance of vimentin and the additional expression of cytokeratin subtypes 8 and 18, as well as the negative staining for epithelial membrane antigen, accorded with results previously reported, for ovarian granulosa cell tumours; the lack of expression of desmoplakin, however, was a distinctive feature. Together with negative staining for leucocyte common antigen, the antigen pattern facilitates the differential diagnosis between granulosa cell tumour and undifferentiated carcinoma or gonadal lymphoma, although its suitability for differentiating within the group of gonadal stromal tumours seems to be limited. The small growth fraction, shown by the monoclonal antibody Ki-67, is typical of the clinical behaviour of granulosa cell tumours. The expression of oestrogen and progesterone receptors, also recently found in testicular Leydig cell tumours, may provoke new approaches to the management of testicular granulosa cell tumours, as well as a new hypothesis on the development of these tumours. 