An unusual case of renal cancer showing mixed tumor response to interferon

A patient with renal cell carcinoma, recurrent in the renal bed and metastatic to the lung parenchyma, hilar lymph nodes, and ilium bone, showed a complete response to 12 months of treatment with human diploid fibroblast interferon. However, concurrently with clinical and pathologic resolution of the metastatic and recurrent tumor at known sites, a brain metastasis developed, which was not clinically or radiologically apparent during his lifetime. At autopsy, there was no evidence of metastatic renal cell carcinoma at the known sites of disease. In the brain, there was a massive fresh intracerebral hemorrhage originating in a small focus of metastatic renal cell carcinoma. Possible explanations for these mixed responses to interferon and this curious phenomenon are discussed.