Metastatic Renal Cell Carcinoma as Solitary Subcentimeter Polypoid Gastric Mucosal Lesions: Clinicopathologic Analysis of Five Cases.

The stomach is an uncommon site for metastatic carcinoma. Approximately 6% of renal cell carcinomas (RCCs) may metastasize to the stomach. The majority of the reported metastatic RCCs in the stomach presented as large masses or ulcers greater than a centimeter in size. It is very rare to encounter metastatic RCC as a solitary small polypoid gastric mucosal lesion.In this study, we collected surgical pathology cases of gastric metastasis from RCC that measured 1.0 cm or less at the time of endoscopy. The clinicopathological characteristics were analyzed.Five patients with subcentimeter metastatic RCC involving the gastric mucosa were identified. The clinical presentation for upper endoscopic examination was non-specific. Two of the five patients did not have a known history of RCC. In the three patients with a previous history of RCC, the interval from primary RCC diagnosis to the detection of gastric mucosal metastasis was 5, 6, and 10 years, respectively. Endoscopically, all the lesions were solitary, ranging in size from 0.4 to 1 cm. Histologically, all five cases were of the clear cell type consisting of a bland clear cell proliferation within the lamina propria. Although the tumor cells were relatively bland, the presence of clear cytoplasm, nuclear membrane irregularity, occasional enlarged hyperchromatic atypical nuclei, and destructive growth in the center of the lesion should promote immunohistochemical workup. Immunohistochemically, the RCC cells exhibited at least patchy immunoreactivity for cytokeratin and RCC markers. In two cases, there were many CD68 positive foamy histiocytes intermingled with the tumor cells.Metastatic RCC can rarely present as subcentimeter polypoid gastric mucosal lesions. The remote or unknown history of RCC, the non-specific endoscopic appearance, and the bland histological features may lead to a potential diagnostic pitfall. It is of importance to raise the awareness of such an unusual presentation of metastatic RCC in the stomach and to include metastatic RCC in the differential diagnosis for gastric mucosal polyps with clear cell morphology.