Small (<4 cm), Unclassified Renal Cell Carcinoma Presenting with Initial Bone Metastasis: A Case of a Metastatic Lesion Missed at the Initial Diagnosis
A 49-year-old male presented with an incidentally detected right renal mass on a health examination. The patient had no symptoms or signs associated with the renal mass but presented with mild anemia (hemoglobin, 11.6 g/dl) and elevated alkaline phosphate (170 U/l).\nAn abdominal CT performed in another hospital showed a 3-cm right renal mass with a homogenous pattern and slight enhancement compared with the common clear cell RCCs (). MRI showed iso-intensity on the T1 weighted image and low signal intensity on the T2 weighted image. Furthermore, an osteoblastic lesion on the right iliac bone was present, but we did not detect the lesion at that time ().\nWe suspected a hypovascular renal tumor such as papillary RCC and performed laparoscopic radical nephrectomy. The surgery was uneventful and the final pathology confirmed unclassified RCC of Fuhrman grade II, pT1aNxMx ().\nTwo months after surgery, the patient came to the emergency room with nausea, vomiting, and fever (38.7℃). Laboratory examination showed anemia (hemoglobin, 8.6 g/dl) and elevated alkaline phosphate (404 U/l), lactate dehydrogenase (657 U/l), and C-reactive protein (15.33 mg/dl). The patient's coagulation profiles were prolonged (activated partial thromboplastin time, 60.5 seconds; prothrombin time, 15.3/75/1.20 sec/%/international normalized ratio). To find the fever focus, abdominal and neck CT was performed, which revealed multiple osteoblastic bone metastases and several enlarged neck lymph nodes. Given that we had not previously detected the synchronous right iliac bone metastasis, we initially suspected a hematologic disorder such as multiple myeloma or myelophthisis. To rule these out, a peripheral blood smear was done; it revealed a rouleaux formation. However, bone marrow aspiration and bone biopsy showed metastasis of RCC. Subsequent review of the initial CT and MRI revealed the synchronous bone metastasis.\nBecause the primary histology was the nonclear cell type, temsirolimus was offered to the patient for first-line therapy. Thirteen cycles of temsirolimus (25 mg weekly) was administered to the patient. The latest follow-up positron emission tomography showed newly developed liver and left adrenal metastases and increased bone metastasis (). We recommended interferon plus vinblastine for second-line therapy. The patient refused further chemotherapy and was instead treated conservatively. Finally, the patient died of the disease.