Coexistence of Multiple Myeloma and Clear Cell Renal Cell Carcinoma: A Case Series and Review of Literature

Renal cell carcinoma (RCC) and multiple myeloma (MM) represent distinct malignancies with disparate origins and clinical presentations, yet emerging evidence suggests a potential association between them, evidenced by a higher-than-expected co-occurrence rate. Shared genetic predispositions, immune dysregulation, paraneoplastic syndromes, and cytokine-mediated mechanisms, particularly involving interleukin-6 from RCC cells, and treatment-related factors, such as chemotherapy-induced genomic instability, may contribute to MM development or progression. The presence of lytic lesions in a patient with prior RCC may simulate bone metastasis, thus leading to a diagnostic pitfall with potentially adverse clinical implications. Here, we describe two patients, a 52-year-old lady and 66-year-old gentleman who were incidentally found to have RCC-MM coexistence. In our two reported cases, the discovery of the neoplasias was synchronous, which rules out the hypothesis of secondary cancer induced by chemotherapy or radiotherapy. Vigilant monitoring and personalized management strategies are essential, necessitating further research to elucidate molecular mechanisms and inform clinical practice.