Complicated variation of simple renal cyst usually means malignancy: results from a cohort study

Currently, simple renal cysts (SRCs) are not considered to warrant follow-up or specific treatment unless a patient presents symptomatically. By demonstrating malignant transformation of SRCs, we urge regular follow-up and timely surgical treatment in affected patients.

From September 2002 to September 2010, we treated 31 cases of renal cell carcinoma derived from SRCs. Among these patients, in 14 cases a SRC was radiographically detected by computed tomography (CT) or magnetic resonance imaging (MRI) prior to operation, and malignant tumors were detected by pathological analysis following laparoscopic cyst decortication; 13 of these patients received supplementary radical nephrectomy within 2 months, whereas one patient chose to receive active surveillance. The other 17 patients exhibited SRCs and were monitored by ultrasound for over 6 months; surgical treatment was chosen if a complicated variation of SRCs was found during surveillance, detected by ultrasound, and confirmed by CT or MRI. Median follow-up was 60 months (30 to 126 months). All data analyzed were collected with informed consent, and the study was approved by the ethical committee of our institute.

Pathological studies confirmed early-stage clear-cell renal cell carcinoma in all of the cases, with Fuhrman grade I to III. In decortication-detected malignancies, supplementary radical nephrectomy exhibited residual tumor in 7 out of 13 cases; the patient who chose active surveillance remains free of recurrence for 78 months, and all other patients survived without disease at the last follow-up.

Renal cell carcinoma may be detected incidentally in SRCs, and more attention should be paid to complicated variations of SRCs during surveillance, owing to the extremely high probability of malignancy. This interesting but alarming phenomenon might urge regular follow-up and timely surgical treatment in affected patients.