Renal cell carcinoma (RCC) is known to metastasize to the lungs, liver, and bones, with gastrointestinal metastases being exceedingly rare. This case report presents the unusual occurrence of a gastrointestinal stromal tumor (GIST) found concurrently with renal cell carcinoma (RCC), initially suspected to be a small bowel metastasis of RCC. The clinical, radiologic, and pathological features of these two separate malignancies are discussed, emphasizing the challenges in diagnosis and management.

A 72-year-old female with mild weight loss of 2-3 kg underwent imaging studies, including a CT scan, which revealed a right renal mass measuring approximately 5 cm. A subsequent PET scan showed uptake in the small bowel, raising concern for small bowel metastasis. The patient underwent a right nephrectomy and small bowel resection for further evaluation. Pathology from the nephrectomy and small bowel resection was reviewed to determine the nature of the renal and small bowel masses.

Pathological examination of the right nephrectomy specimen confirmed clear cell renal cell carcinoma (RCC), measuring 48 mm, pT1b, ISUP nucleolar grade 3, confined to the kidney, with clear surgical margins and no adrenal involvement. The small bowel resection revealed a gastrointestinal stromal tumor (GIST), spindle cell type, measuring 21 mm, with unclear margin status, categorized as pT2 and assigned a prognostic risk stratification category 2.

This case highlights the rare occurrence of concurrent RCC and GIST in a single patient, underscoring the importance of differentiating between primary tumors and metastatic disease. Despite the PET scan uptake suggesting a small bowel metastasis from RCC, further pathological examination revealed a separate, incidental GIST. This case emphasizes the need for a comprehensive diagnostic approach when evaluating possible metastases in patients with malignancies, particularly in unusual cases where concurrent malignancies may be present. Multidisciplinary evaluation and careful diagnostic workup are crucial in the management of such complex cases.