AQP1 and renal cell carcinoma: The eleven patients with positive AQP1 signals were determined to have clear cell renal cell carcinoma (n = 5), papillary renal cell carcinoma (n = 4), chromophobe RCC (n = 1), oncocytoma (n = 1), cystic nephroma (n = 1), and unclassified RCC (n = 1).