A contemporary series of renal masses with emphasis on recently recognized entities and tumors of low malignant potential: A report based on 624 consecutive tumors from a single tertiary center.

INTRODUCTION: A number of new renal tumor entities have been recognized by the 2016 World Health Organization classification of urologic tumors. The classification includes tumors with different behavior and introduces one tumor with low malignant potential, the multilocular cystic clear cell renal cell neoplasm of low malignant potential (mcCCRCNLMP). However, some categories still labeled as "carcinoma", such as clear cell papillary renal cell carcinoma (CCPRCC), renal angioleiomyomatous tumor (RAT), and tubulocystic carcinoma (TCRCC), all with a particularly good prognosis when diagnosed as low stage, show no malignant behavior: in fact, no metastases have been reported in these categories when surgically excised. Current experience is limited to supporting these neoplasms as benign entities although, recent literature data is defining these entities as "low malignant potential tumors". MATERIAL AND METHODS: We conducted a search through our files on a consecutive series of 624 renal tumors diagnosed over a period of 2 years to address the incidence of this category of tumors. RESULTS: Applying strict histological criteria, the "low malignant potential" tumors, comprised 7% of renal masses that are less than 4cm in size and 3.8% of renal masses measuring 4-7cm in the series of 624 renal tumors. When benign tumors are taken into considerations, the benign and "low malignant potential tumors" represent about one third of renal masses <4cm and one sixth of renal masses between 4 and 7cm. All these cases have not shown recurrence or metastasis at follow-up, mean follow-up of 18 months (range 6-30 months). CONCLUSIONS: This information may assist urologists in developing guidelines for counseling and proper clinical management for patients with "low malignant potential" tumors or small renal masses.