Tumor-to-tumor metastasis: report of two cases of renal cell carcinoma metastasizing to microcystic serous cystadenoma of the pancreas.

Metastatic cancer to the pancreas accounts for less than 2% of all pancreatic malignancies. In contrast to other metastatic tumors, renal cell carcinoma (RCC) has a propensity to metastasize as a solitary pancreatic lesion. While symptomatic patients may present with obstructive jaundice, abdominal pain, or gastrointestinal bleeding, the diagnosis of metastatic pancreatic involvement is often made in asymptomatic patients, during follow-up evaluation in the aftermath of an initial diagnosis of renal cell carcinoma. Microcystic serous cystadenoma of the pancreas is an uncommon pancreatic exocrine neoplasm that morphologically resembles conventional (clear cell) RCC, in so far as both tumors are characterized by neoplastic cells with clear cytoplasm, relatively uniform nuclei and scant associated tumor stroma. Herein, we report 2 immunohistochemically confirmed cases of unsuspected metastatic RCC to the pancreas, with the metastatic tumor in each case confined to a preexisting microcystic serous cystadenoma of the pancreas.