Renal Clear Cell Carcinoma with Unknown Primary: Is It Real Entity or Just Hypothesis?

Renal cell carcinoma (RCC) is a common type of cancer, and about 25% of patients are diagnosed at an advanced stage. Bone metastasis is common in RCC, but instances of bone metastases without a primary kidney tumour have rarely been reported. Here, we report a case of a 56-year male patient who presented with extensive bone metastases. The biopsy was reported as clear cell RCC and no primary renal tumour was detected by positron emission tomography and magnetic resonance imaging. Pazopanib was initiated and progression was detected in the 6th month of treatment. Nivolumab was initiated as second line therapy. In the literature, primary unrecognised RCC cases are found only as case reports. This case highlights the importance of clinicians' consideration of possible metastatic RCC in a patient with pathologically diagnosed clear cell carcinoma, even if no primary renal tumour is identified.