Aberrant expression of p27^Kip1-interacting cell-cycle regulatory proteins in ovarian clear cell carcinomas and their precursors with special consideration of two distinct multistage clear cell carcinogenetic pathways

We have previously reported that alterations of p27^Kip1-interacting cell-cycle proteins frequently occur during the development of endometriosis-associated ovarian clear cell adenocarcinoma (CCA; Yamamoto et al., Histopathology in press, 20). However, CCA also occurs in association with clear cell adenofibroma (CCAF). In this study, the expressions of p27^Kip1-interacting proteins, i.e., p27^Kip1, Skp2, Cks1, cyclin A, cyclin E, and the Ki-67 labeling index (LI), were analyzed in 25 CCAFs (11 benign and 14 borderline) and 15 CCAF-associated CCAs, and compared with the expression status of each protein in the 23 previously studied endometriosis-associated CCAs. Although aberrant expression of all p27^Kip1-interacting proteins was more frequent in the CCAF-associated CCAs than in the benign CCAFs, statistical significance was found only for Cks1 overexpression. The frequencies of p27^Kip1 downregulation and overexpression of Skp2 and cyclin A were significantly lower in CCAF-associated than in endometriosis-associated CCAs (P < 0.05, respectively). The frequencies of p27^Kip1 downregulation and Skp2 overexpression in borderline CCAFs were significantly lower than those in atypical endometriosis components in endometriosis-associated CCAs (P < 0.05, respectively). Mean Ki-67 LI increased significantly through benign (4.9%) to borderline (11.1%) CCAF and to CCAF-associated CCA (30.6%), but the latter two values were significantly lower than those in atypical endometriosis (21.4%) and endometriosis-associated CCA (46.9%; P < 0.05, respectively). These data suggest that accumulated alterations of p27^Kip1-interacting proteins may accelerate the development of CCAs regardless of their carcinogenetic pathways, but that tumor cells in the CCAF-associated pathway appear to show slower cell-cycle progression than those in the endometriosis-associated pathway, possibly accounting for the distinct clinicopathological features of the two CCA subtypes.