Tiny gastric metastasis from clear cell renal cell carcinoma mimicking fundic gland-type adenocarcinoma

Gastric metastasis from clear cell renal cell carcinoma is uncommon and may mimic a primary gastric neoplasm. We report a man in his late sixties with a 0.6-cm reddish protruding gastric lesion initially interpreted as fundic gland-type adenocarcinoma, mainly on the basis of morphology and an initial immunohistochemical panel. Targeted forceps biopsy showed small nests of tumor cells in the lamina propria. Endoscopic submucosal dissection, performed under the working diagnosis of early primary gastric neoplasia, showed no residual malignancy, probably because the minute focus had been largely removed by biopsy. Subsequent nephrectomy confirmed clear cell renal cell carcinoma. Additional immunohistochemistry of the gastric biopsy showed PAX8, CAIX, CK8/18, partial CD10 and focal RCC marker positivity, supporting gastric metastasis. This case highlights the importance of renal-lineage immunohistochemistry in small gastric lesions with unusual morphology.