Multilocular cystic renal cell carcinoma : a report of 45 cases of a kidney tumor of low malignant potential.

The 2004 World Health Organization (WHO) classification of kidney tumors recognizes multilocular cystic renal cell carcinoma (MCRCC) as a rare variant of clear cell renal cell carcinoma with a good prognosis. Available information on its clinical significance is limited. The study cohort included 45 MCRCC cases classified according to 2004 WHO criteria obtained through a multi-institutional international search. Most patients had unilateral MCRCC with no side predominance that was found incidentally; 62% were men, but women had tumors at an earlier age (P = .385). MCRCC occurred slightly more often in men than in women (1.7:1). At diagnosis, 82% of patients had stage T1 and 16%, stage T2; 1 patient had stage T3. The Fuhrman grade was 1 (62%) or 2 (38%), with smaller tumors (<or=4 cm) most likely Fuhrman grade 1 (P = .911). All 45 patients were alive with no evidence of disease at mean follow-up of 66.1 months, confirming an extremely good prognosis after surgery and a 5-year disease-specific survival rate of 100%. To rename this tumor as multilocular cystic renal cell neoplasm of low malignant potential might help urologists approach the patients conservatively.