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Alterations of cell cycle regulators affecting the RB pathway in nonfamilial retinoblastoma
1Department of Pediatrics and School of Public Health, Columbia University, New York, NY 10021, USA.
Abstract:
We undertook the present study to examine alterations affecting the RB pathway in the G1 checkpoint and to determine their potential clinical significance in children affected with nonfamilial retinoblastoma. Using immunohistochemistry, patterns of expression of pRB, p16/INK4A, and E2F1 were analyzed in tissue from a cohort of 86 well-characterized patients with nonfamilial retinoblastoma diagnosed at the "Instituto Nacional de Pediatria" in Mexico City. The relationship of these phenotypes to proliferative index was assessed by analysis of Ki67 antigen expression. pRB expression was found in 11 (13%) cases. Using a hypophosphorylated specific pRB antibody, we observed low levels of underphosphorylated pRB expression in only 1 of 9 evaluable positive cases. These data suggest that the detected pRB products were hyperphosphorylated 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 significantly associated with undetectable p16 expression (odds ratio, 10.8; 95% confidence interval, 1.4-81.3; P =.03). All tumors showed nuclear immunoreactivities for E2F1 and Ki67. Increased Ki67 proliferative index was associated with increased staining for E2F1 (r =.44; P =.008) and increasing clinical stage (P =.03). Among children with unilateral disease, the mean Ki67 proliferative index was significantly higher in children with advanced clinical disease (stages 3 and 4) (mean 81.25; SD 6.78) than in those with earlier stage disease (mean 69.50; SD 9.45) (P = 0.001). Among children with bilateral disease, however, the mean proliferative index was not significantly higher for children with advanced clinical stage. When examining all cases together, there was a significant trend toward increasing proliferative index with increasing clinical stage (P =.03). In unilateral tumors, we also found that presence of detectable pRB was associated with a lower percentage of cells expressing E2F1 (46.7% v 70.8%) (P = 0.05), whereas there was no association between presence of pRB and E2F1 among bilateral tumors. We have found that expression of some of the cell cycle markers examined varies according to laterality, suggesting underlying differences in the capacity for cell cycle regulation between these 2 forms of the disease. Differences in capacities for cell cycle regulation may account for some differences in clinical behavior. Thus, the inclusion of molecular markers may become useful adjuncts to clinicopathological staging and subsequent determination of therapy.
Insights
RB pathway alterations in nonfamilial retinoblastoma were studied. Reduced functional pRB and linked cell cycle dysregulation correlate with tumor stage and laterality, suggesting molecular markers aid clinical staging.
Area of Science:
- Oncology
- Molecular Biology
- Cell Cycle Regulation
Background:
- Retinoblastoma (RB) pathway is crucial for cell cycle control.
- Alterations in RB pathway are implicated in retinoblastoma development.
- Understanding these alterations is key for improved diagnosis and treatment.
Purpose of the Study:
- To investigate RB pathway alterations in the G1 checkpoint in nonfamilial retinoblastoma.
- To determine the clinical significance of these alterations in pediatric patients.
- To correlate molecular findings with tumor proliferation and clinical stage.
Main Methods:
- Immunohistochemistry used to analyze pRB, p16/INK4A, and E2F1 expression in 86 retinoblastoma tissues.
- Ki67 antigen expression assessed to determine proliferative index.
- Statistical analyses performed to correlate molecular markers with clinical parameters.
Main Results:
- Reduced functional pRB (hyperphosphorylated) observed in most cases.
- Undetectable pRB levels significantly associated with undetectable p16 expression.
- Increased Ki67 proliferation index correlated with E2F1 expression and advanced clinical stage.
- Differences in RB pathway markers noted between unilateral and bilateral retinoblastoma.
Conclusions:
- RB pathway dysregulation is common in nonfamilial retinoblastoma.
- Molecular markers like pRB, p16, and E2F1 show differential expression and clinical correlation.
- Laterality influences cell cycle regulation, impacting clinical behavior.
- Molecular markers may enhance clinicopathological staging and guide therapy decisions.