Atypical Renal Cysts: A Morphologic, Immunohistochemical, and Molecular Study

There is a lack of standardized nomenclature for renal cysts lined by multiple cell layers or with short papillary projections but without nests of epithelial cells within the stroma. We retrieved 29 cases (15 nephrectomies, 14 partial nephrectomies) from the surgical pathology files of Johns Hopkins Hospital from 1993 to 2014 and performed immunohistochemistry for CK7, alpha-methylacyl-CoA racemase (AMACR), CAIX, and CD10 and fluorescence in situ hybridization for trisomy 7 and 17 and 3p deletion. The mean age at excision was 58 years (range, 29 to 80 y) with 16 men and 13 women. Mean size was 2.9 cm (range, 0.3 to 10 cm). The cysts were grouped by their morphology into (1) clear cell, (2) eosinophilic stratified, and (3) eosinophilic papillary. By immunohistochemistry, 7/9 (78%) of the clear cell cases were diffusely positive for both CK7 and CAIX resembling the pattern seen in clear cell papillary renal cell carcinoma. The majority of eosinophilic stratified (4/6; 67%) and eosinophilic papillary (12/14; 86%) cases were positive for CK7 and had variable staining for AMACR, CD10, or CAIX, suggesting a differentiation more aligned with papillary renal cell carcinoma. The most common molecular alterations detected were trisomy 17 (n=6) and trisomy 7 (n=4). One case showed deletion of chromosome 3p. Clinical follow-up information was available in 23 patients; 20 were alive with no evidence of disease after a median follow-up of 20 months (range, 3 to 120 mo), 1 patient was dead due to metastatic lung cancer, 1 of sepsis, and 1 of unknown reason. Atypical renal cysts present as complex radiologic lesions, as secondary lesions in patients with a renal mass, or in a background of chronic renal disease. These atypical cysts appear heterogenous, and some follow in their morphology and immunoprofile with well-established renal tumors. The presence of 3p deletion and trisomy 7/17 suggests that in some cases they may be precursors of renal cell carcinoma. Longer follow-up with more cases is needed, but on the basis of our data, these lesions should not be diagnosed as carcinoma.