Tumor-to-tumor metastasis: report of 2 cases of metastatic carcinoma to angiomyolipoma of the kidney.

Tumor-to-tumor metastasis is a rare phenomenon. Renal cell carcinoma is the most common recipient of tumor-to-tumor metastasis in malignant tumors. However, renal angiomyolipoma has not been reported to be a recipient. Here we report 2 cases of tumor-to-tumor metastasis to renal angiomyolipoma. In one case, the donor tumor originated from neuroendocrine carcinoma of the pancreas, and in the other case the donor tumor was from adenocarcinoma of the lung. The donor tumors showed morphologic features that did not easily fit into renal angiomyolipoma, and they also demonstrated patterns of immunoreactivity consistent with the primary tumors rather than with renal angiomyolipoma. To our knowledge, these are the first reported cases of tumor-to-tumor metastasis to renal angiomyolipoma. An awareness of this phenomenon is important to avoid an incorrect diagnosis when encountering unusual morphologic features in renal angiomyolipoma.