Renal oncocytomas are the second most common benign renal tumours and they originate from the collecting tubules. They appear genotypically very similar to chromophobe renal cell carcinomas (chRCC), which also contain eosinophilic cells. Oncocytomas are often found incidentally on routine imaging and can be biopsied safely. However, the majority of renal tumours are treated without tissue diagnosis, as there are concerns over reliability of biopsy results. A retrospective, single centre study was carried out looking at patients between January 2003 and December 2014 with histological confirmation of oncocytoma or chRCC after biopsy or resection. Only those with serial imaging 12 months or more were included. Ninety-five patients qualified for this study. Oncocytomas were found to have grown by a median of 0.4 cm after 34 months of median imaging follow-up. During the study period 81 oncoctyomas were identified, 75% of these increased in size whilst 19% decreased in size and 6% remained unchanged. Of the 61 tumours that increased in size, 24 grew 0.5 cm or less and 40 had grown 1 cm or less. At the three-year mark, 29 of 39 tumours (74%) increased in size, eight (21%) decreased and two (5%) remained stable. Fourteen chRCC were identified with a 25-month median imaging follow-up period and median growth was 0.5cm. Sixty-four percent increased in size where five reduced in size. In the group that increased in size, two grew by 0.5cm or less and four grew by 1cm or less. Six lesions made the three-year mark, four (66%) increased in size, one (17%) decreased in size and one (17%) was stable. This study shows that renal tumours with oncocytic features can be managed safely with active surveillance and regular imaging.

Active surveillance for renal neoplasms with oncocytic features is safe.
Richard PO, Jewett MAS, Bhatt JR, et al.
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