Alterations of cell cycle regulators affecting the RB pathway in nonfamilial retinoblastoma

We undertook the present study to examine alterations affecting the RE path way in the G1 checkpoint and to determine their potential clinical signific ance in children affected with nonfamilial retinoblastoma, Using immunohist ochemistry, patterns of expression of pRB, p16/INK4A, and E2F1 were analyze d in tissue from a cohort of 86 well-characterized patients with nonfamilia l retinoblastoma diagnosed at the "Instituto Nacional de Pediatria" in Mexi co City. The relationship of these phenotypes to proliferative index was as sessed by analysis of Ki67 antigen expression. pRB expression was found in 11 (13%) cases. Using a hypophosphorylated specific pRB antibody, we observ ed low levels of underphosphorylated pRS expression in only 1 of 9 evaluabl e positive cases. These data suggest that the detected pRB products were hy perphosphorylated and thus had decreased functional activity. Increased p16 nuclear expression was found in only 6 tumors. No tumors showed deletions or mobility shifts of the INK4A gene. Undetectable pRB levels were signific antly associated with undetectable p16 expression (odds ratio, 10.8; 95% co nfidence interval, 1.4-81.3; P = .03). All tumors showed nuclear immunoreac tivities for E2F1 and Ki67, Increased Ki67 proliferative index was associat ed with increased staining for E2F1 (r = .44; P = .008) and increasing clin ical stage (P = .03), Among children with unilateral disease, the mean Ki67 proliferative index was significantly higher in children with advanced cli nical disease (stages 3 and 4) (mean 81.25; SD 6.78) than in those with ear lier stage disease (mean 69.50; SD 9.45) (P = 0.001). Among children with b ilateral disease, however, the mean proliferative index was not significant ly higher for children with advanced clinical stage. When examining all cas es together, there was a significant trend toward increasing proliferative index with increasing clinical stage (P = .03). In unilateral tumors, we al so found that presence of detectable pRB was associated with a lower percen tage of cells expressing E2F1 (46.1% nu 70.8%) (P = 0.05), whereas there wa s no association between presence of pRB and E2F1 among bilateral tumors. W e have found that expression of some of the cell cycle markers examined var ies according to laterality, suggesting underlying differences in the capac ity for cell cycle regulation between these 2 forms of the disease. Differe nces in capacities for cell cycle regulation may account for some differenc es in clinical behavior. Thus, the inclusion of molecular markers may becom e useful adjuncts to clinicopathological staging and subsequent determinati on of therapy. Copyright (C) 2001 by W.B. Saunders Company.