Pigmented renal cell carcinoma: accumulation of abnormal lysosomal granules

Five cases of renal cell carcinoma (RCC) with abnormal pigmentation have been examined by histochemical, immunohistochemical and ultrastructural methods.

Compared with conventional RCCs, there was no difference in histological findings of each case, except for the presence of pigmented cells. In three cases, tumour cells possessing various sized brown granules with neuromelanin-like features were scattered throughout the tumour. The granules observed in one of the others were angulated lysosomes and in another tumour cells in the pigmented areas possessed the granules closely resembling those of granular cell tumour. However, melanosome or neurosecretory granules could not be detected in any of the cases examined. In three cases, some of these abnormal granules showed a weak acid phosphatase activity. On immunohistochemical examination, tumour cells showed a positive immunoreaction for epithelial markers and lacked any antigens suggesting neuroectodermal or neuroendocrine differentiation. The granules in three cases were faintly positive for lysozyme and KP-1.

These findings indicate that abnormal pigmentation of RCCs examined in this study is attributed to accumulation of abnormal lysosomal granules in the neoplastic cells.