Light micrograph section through human kidney tissue showing Clear cell renal cell carcinoma. Renal cell carcinoma RCC is a kidney disease that originates in the lining of the proximal convoluted tubule, a part of the small tubes in the kidney that transport primary urine. It is the most common form of kidney cancers, with about 90% being renal cell carcinomas. Clear cell renal cell carcinomas, ccRCC, occurs when cells in the kidney quickly increase in number, creating a lump or mass.