Histological Classification of Proliferative Cysts in Acquired Cystic Disease of the Kidney : Renal Cell Carcinoma in Dialysis Patients as a Model of Multistep Carcinogenesis

Long-term dialysis is known to induce development of renal cell carcinoma (RCC) from acquired cystic disease of the kidney (ACDK), but no pathological patternization has been determined for the presumably multistep carcinogenesis. Proliferative cystic epithelia in ACDK were pathologically classified to evaluate multistep carcinogenesis, and frequency analysis suggested a tentative process for multistep carcinogenesis. Approximately 100 cysts each from 20 surgically resected RCCs with ACDK (total, 1,752 cysts) were analyzed. Prior to analysis, 300 randomly selected sites of proliferative cysts underwent histological classification of cystic epithelia. Type I represented single-layer cystic epithelia (Ia, flat ; Ib, cuboidal). Proliferative cystic epithelia comprised : Type II, pseudostratification ; Type III, papillary proliferation; and Type IV, cells forming networks among epithelia. Single-layer epithelia comprised 81.7% Type la and 18.3% Type Ib. All proliferative epithelia intermingled with single-layer cystic epithelia, with 96.3% accompanying Type Ib. Compared with only 1% of Type Ia, 65% of Type Ib showed proliferative lesions (Type II, >50% ; Type II + III, 21% ; Type II + IV, 18%). Histological classification appeared valid. Presence of Type Ib may be critical to proliferative lesion development. Carcinogenesis may involve Type Ib pseudostratification followed by morphological changes involving papillary formations and anastmosing networks