Background Renal cell carcinoma (RCC) is the most prevalent kidney malignancy in adults, accounting for 80-85% of primary renal tumors. In advanced-stage RCC, up to 30% of patients develop skeletal metastasis, causing severe bone pain and reduced quality of life. Bone metastases are often due to increased blood flow and red marrow density in highly vascularized long and flat bones. While acrometastasis—metastasis to distal bones—is rare, the high vascularity and marrow density in adult hand bones may contribute to its occurrence in 0.1-0.3% of cases. This report describes a case where RCC recurrence was indicated by left hand acrometastasis one year after initial malignancy diagnosis.

Case Presentation A 65-year-old man with a history of renal cell carcinoma presented with persistent pain and swelling in the distal left long finger for 6 months. Examination revealed tenderness, swelling, and erythema in the distal phalanx, but no issues in the shoulder, elbow, or forearm. An incisional biopsy confirmed metastatic RCC to the distal phalanx, with X-rays showing a destructive process and MRI revealing an enhancing subcutaneous mass with mild erosive changes. Orthopedic consultation led to a distal interphalangeal joint disarticulation of the finger. Post-surgery pathology confirmed metastatic RCC, and the patient was later admitted to hospice care.

Discussion Acrometastasis in RCC results from hematogenous rather than lymphatic spread. Cancer cells must survive in the systemic circulation, invade the sinusoidal vessels, and establish a blood supply in the bone marrow to initiate metastasis. Key factors include heparanase, which promotes metastasis by degrading extracellular matrix components, and RANKL, which facilitates cancer cell migration and osteoclastogenesis. Both RANKL and its receptor RANK, as well as the decoy receptor OPG, are involved in bone remodeling and metastatic processes.

Clinical signs of acrometastasis include erythema, pain, swelling, and functional impairment, but can mimic conditions like osteomyelitis or gout. Early and accurate diagnosis is crucial, necessitating imaging studies and tissue biopsies when possible. Distinguishing acrometastasis from other conditions is essential for appropriate treatment, given its poor prognosis with a median survival of 6 months.

The rarity of acrometastasis means there is no standard treatment protocol; management focuses on palliation, including pain control, resection, and maintaining function. Resection might involve ray amputation or more conservative approaches like radiation for large, inoperable lesions. Though prognosis is generally poor, solitary osseous RCC lesions may have a better outcome with wide resection and nephrectomy.