Acquired Cystic Disease-associated Renal Cell Carcinoma (ACKD-RCC)-like Cysts.

Acquired cystic disease-associated renal cell carcinoma (ACKD-RCC), originally described by Tickoo and colleagues, is found exclusively in patients with end-stage renal disease. Tickoo and colleagues noted: "Many of the tumors (16 of 24 dominant tumors) appeared to arise in a cyst, most often completely filling the cystic space. The cells lining such cysts were morphologically similar to those in the rest of the tumor." Subsequent literature lacks analysis of cysts lined by cells identical to ACKD-RCC, yet lacking areas of solid growth. The current study evaluates 16 cases ACKD-RCC-like cysts. All specimens were nephrectomies and occurred in the setting of end-stage renal disease. Of the 16 cases, 9 were in men. Patient's ages ranged from 32 to 66 years (median: 57). The cysts ranged in size from 0.2 to 2.5 cm. Twelve cases had unilateral cysts with the remaining 4 seen in both kidneys. Nine cysts were multilocular, 6 unilocular, and 1 consisted of closely clustered cysts. The atypical cysts showed architectural variation. One cyst was lined by a single layer of atypical cells (1/16), whereas in the majority these were either focally lined by 2 to 4 cell layers of atypical cells (6/16 cases) or showed occasional short papillary formations (9/16). Calcium oxalate crystals were noted in cyst walls in 7/16 cases. A total of 12/16 cases had separate RCCs (2 cases with 2 RCCs each; 1 case with 3). Carcinoma ranged in size from 3 mm to 5 cm in the largest dimension: 4 were pT1 ACKD-RCC; 5 were pT1 papillary RCC; 5 were pT1 clear cell papillary RCC; 1 was pT3 clear cell RCC; and 1 pT1 unclassified. Our study formally analyzes for the first time in the literature atypical cysts lined with vacuolated cells with eosinophilic cytoplasm that are likely the earliest precursors of ACKD-RCC. When these cysts are encountered, especially ones that are multilocular or clustered, they may be misdiagnosed as ACKD-RCC. ACKD-RCC-like cysts should be recognized as a distinct entity from ACKD-RCC, defined by the lack of any solid nodular growth within the cyst.