Diagnostic Pitfall of Lytic Bone Lesions: A Case of Chromophobe Renal Cell Carcinoma Coexisting With Multiple Myeloma

The coexistence of renal cell carcinoma (RCC) and multiple myeloma (MM) is rare and presents a significant diagnostic challenge, particularly when patients present with back pain and lytic bone lesions. Several case series and reports have documented a reciprocal relationship between the two malignancies, which may be attributed to shared etiological factors, analogous cytokine-mediated growth mechanisms, and converging clinical presentations. We report the case of a 66-year-old man diagnosed with chromophobe RCC who presented with persistent back pain and was ultimately diagnosed with coexisting MM.