Detection of human papillomavirus DNA in retinoblastoma samples: a preliminary study

Association of peripheral vestibular disorder with human papillomavirus infections

PURPOSE

Emerging research indicates that viral infections may contribute to the development of certain vestibular disorders. This study aimed to explore the association of peripheral vestibular disorders (PVDs) with human papillomavirus (HPV) using a comprehensive population-based dataset from Taiwan's Longitudinal Health Insurance Database 2010.

METHODS

We examined a cohort comprising 94,215 patients with a new diagnosis of PVDs and 471,075 propensity-score matched controls, utilizing propensity score matching. Multiple logistic regressions were carried out to evaluate the potential link between HPV infections and PVDs.

RESULTS

Results revealed a statistically significant higher prevalence of prior HPV infections in patients with PVDs (10.6%) than controls (7.7%). The adjusted odds ratio for prior HPV infections in patients with PVDs was 1.440 (95% CI = 1.407 ~ 1.474) compared to the controls. Additionally, we analyzed the association across different types of PVDs: Meniere's disease, benign paroxysmal positional vertigo, vestibular neuritis, and other peripheral vestibular disorders, with adjusted odds ratios of 1.342 (95% CI = 1.253 ~ 1.437), 1.445 (95% CI = 1.359 ~ 1.536), 1.484 (95% CI = 1.370 ~ 1.607), and 1.452 (95% CI = 1.410 ~ 1.494), respectively.

CONCLUSION

The findings of the present study suggest a noteworthy association between HPV infections and PVDs. These insights highlight the importance of further exploring the interplay between HPV and PVDs, which could potentially lead to novel preventative and therapeutic measures in public health.

Human Papillomavirus and Retinoblastoma: Evidence From a Systematic Review and Meta-analysis of Cross-Sectional Studies

Objectives: To study the prevalence and the association of HPV infection in retinoblastoma and to determine the most common genotype presented in RB. Methods: Following the PRIMSA guideline, 14 studies reporting HPV infection in RB acquired from six databases were included. Results: The prevalence of HPV from 941 RB samples was 15.6% [95% confidence interval (CI): 7.3-30]. Mexico followed by India and Brazil had the highest HPV prevalence in RB samples, 61.7% (95% CI: 17-93), 22.5% (95% CI: 9-47), and 12.1% (95% CI: 2-52), in order. HPV 16 was the most common genotype presented in RB samples 23% (95% CI: 9-47), followed by HPV 18 10% (95% CI: 3-30) and the combined HPV 16-18 6% (95% CI: 0-50). We did not find a significant association between HPV and RB [odds ratio (OR): 12.2; 95% CI: 0.65-232; p = 0.09]. However, after removing the largest-weighted study, a significant association between HPV and RB was observed (OR: 45.9; 95% CI; 8.6-245; p < 0.001). Conclusion: HPV prevalence in RB samples was 15% and HPV 16 was the most presented genotype in RB samples. There may be an association between HPV and RB that is needed to be confirmed by high quality future studies. Preventive and treatment measures against HPV infection are essential for the prevention of any possible consequences, in particular, RB.

HPV infections in retinoblastoma: a systematic review

BACKGROUND

Retinoblastoma is the most common primary intraocular malignancy in children less than 4 years. Retinoblastoma (RB) contains about 3%-5% of all childhood cancers. Recent studies demonstrated that interacting between RB tumor suppressor and oncoproteins of DNA tumor viruses such as human papillomavirus (HPV). The objective of the current systematic review study was to present conducted studies in the field of HPV infection and its possible role in retinoblastoma.

METHODS

For this systematic review, all relevant original research studies were assessed by searching in electronic databases include PubMed, Embase, Scopus, Google Scholar, and Web of Science by using relevant keywords. The study was designed based on the PRISMA criteria. All publications with English literature and original researches are considered for screening.

RESULTS

Conducted search results lead to 4070 studies. The title and abstract screening lead to 11 studies. Data extraction was performed on 8 included studies. The prevalence of the HPV was ranged from 0 to 69%, and HPV genotype 16 and 18 were the most detected types. The most used method for the detection of the viruses was PCR, and the most assessed sample was formalin-fixed, paraffin-embedded tissue blocks.

CONCLUSION

The association between HPV and retinoblastoma is still inconsistent. The prevalence of the HPV in RB was ranged from 0 to 69%, which indicates a wide range and highlights the importance of further investigation for more accurate statistical of HPV prevalence in RB. Thus, further worldwide studies of larger sample sizes of cohorts should be investigated to clarify this uncertainty.

Human papillomavirus in retinoblastoma: A tertiary eye care center study from South India

Purpose:

This study is aimed to investigate the presence of Human papillomavirus (HPV) DNA in tumors obtained from sporadic retinoblastoma patients.

Methods:

One hundred six tumor tissues obtained from sporadic RB patients were analyzed for HPV infection by use of both seminested PCR and real-time quantitative PCR.

Results:

Of 106 RB patients, 55 were male and 51 were female. The mean age at diagnosis was 26.77 ± 15.36 (mean ± Std. dev) months. Almost all patients presented with leukocoria. Molecular investigation by different methods revealed no HPV positivity in any tumor genome.

Conclusion:

Our study demonstrates no association between HPV and RB, postulating HPV may not be a major risk factor in the etiology of RB.

Molecular evidence of human papillomaviruses in the retinoblastoma tumor

Retinoblastoma tumor (RB) is one of the most prevalent ocular cancers among children. RB may be caused by inherited mutations in RB1 gene as well as some environmental risk factors. Human papillomaviruses (HPV) are suspected as a risk factor of RB due to their pRb inactivating protein. This study evaluated the molecular prevalence of HPV among the RB tumor specimens in Iran. The RB tumor samples were tested for detection of HPV-L1 gene using a nested-PCR approach, and then followed by sequencing and phylogenetic analysis to reveal HPV types. Overall, there were 61 RB tumor samples; 54/61 (88.5%) had unilateral and 7/61 (11.5%) bilateral RB; 55/61 cases (90.2%) had sporadic non-familial RB tumor. HPV-DNA was detected in 6/61 (9.8%) of patients' tumors; the HPV positive RB cases all had unilateral and unfamiliar sporadic RB tumor. HPV type 16 was the most prevalent type identified across the RB tumor samples (3/61, 4.9%). The rate of detected HPV among the RB specimens seems to be considerable. Further investigations are required to elucidate the exact association between HPV and progression to RB.

Human papillomavirus in ocular malignant tumours: a study from a tertiary eye care centre in North India

OBJECTIVE

The present study aims to detect the presence of human papillomavirus (HPV) in ocular malignant tumours, including retinoblastoma, eyelid squamous cell carcinoma (SCC), and sebaceous gland carcinoma (SGC), in the North Indian population.

DESIGN

Prospective observational non randomized study.

PARTICIPANTS

In this study, 142 prospective cases of ocular malignant tumours (retinoblastoma, SGC, and SCC) were included.

METHODS

HPV was detected by multiplex PCR using PGMY09/11 primers in 142 patients with ocular malignancies. This was followed by genotyping using linear array (reverse hybridization).

RESULTS

Of the 142 tumours studied, 72 were retinoblastoma, 30 SGC, and 40 SCC. The HPV genome was detected in 2.8% (4 of 142) of cases by multiplex PCR; all positive cases (4 of 40) were SCC. Genotyping revealed that all positives belonged to the high-risk HPV16 genotype. HPV-positive SCC patients had better disease-free survival. Retinoblastoma and SGC cases were negative for HPV.

CONCLUSIONS

Low prevalence of HPV in ocular malignancies was observed in this study. The HPV genome was detected only in ocular squamous cell carcinoma cases and these patients were associated with better prognosis. HPV may not have a role in retinoblastoma and SGC in the North Indian population.

Structural changes of the macula and optic nerve head in the remaining eyes after enucleation for retinoblastoma: an optical coherence tomography study

BACKGROUND

To describe objectively the possible structural changes of the macula and optic nerve head in the free eyes of unilateral cured retinoblastoma patients and, also after enucleation using spectral domain optical coherence tomography.

METHODS

A cross sectional study involving 60 patients subdivided into three groups; 15 unilateral RB patients in whom enucleation was indicated as a sole treatment performed earlier in life [(study group (I)], 15 unilateral RB patients who had completely regressed disease with a preserved eye [(study group (II)] and 30 age and sex matched healthy controls. The remaining and free eyes in study groups and right eyes of control group had full ophthalmological examination, static automated perimetry and optical coherence tomography of the macula and optic nerve head.

RESULTS

In study group (II); a significant thinning of total macula, central fovea, ganglion cell layer (GCL), ganglion cell complex (GCC), and some sectors of outer nuclear layer (P- values ≤0.05) was found with no significant difference in peripapillary nerve fiber layer (pRNFL) thickness and optic nerve head parameters compared to the control group and the study group (I). A significantly thickened total macula, GCL, GCC, and pRNFL in study group (I) compared to study group (II). Thickened pRNFL was significantly correlated to standard automated perimetry pattern deviations. No significant difference was found between study group (I) and control group.

CONCLUSION

Retinoblastoma eyes characterized by thinning of central fovea, GCL, GCC compared to the control group. After unilateral enucleation, increased GCC and pRNFL thicknesses were detected compared to retinoblastoma group.

Identification of differentially expressed proteins in retinoblastoma tumors using mass spectrometry-based comparative proteomic approach

In India, retinoblastoma is among the top five childhood cancers. Children mostly present with extraocular extension and high risk features that results in unsatisfactory treatment and low survival rate. In addition, lack of potential therapeutic and prognostic targets is another challenge in the management of retinoblastoma. We studied comparative proteome of retinoblastoma patients (HPV positive and negative (n=4 each) and controls (n=4), in order to identify potential retinoblastoma-specific protein targets. 2D-DIGE coupled MALDI-TOF/TOF mass spectrometry identified 39 unique proteins. Highly deregulated proteins were GFAP,RBP3,APOA1,CRYAA,CRABP1,SAG and TF. Gene ontology (Panther 7.0) revealed majority of proteins to be associated with metabolic processes (26%) and catalytic activity (38%). 8 proteins were significantly upregulated in HPV positive vis-a-vis HPV negative cases. Patient group exhibited 12 upregulated and 18 downregulated proteins compared to controls. Pathway and network analysis (IPA software) revealed CTNNB1 as most significantly regulated signalling pathway in HPV positive than HPV negative retinoblastoma. The trends in transcriptional change of 9 genes were consistent with those at proteomic level. The Western blot analysis confirmed the expression pattern of RBP3,GFAP and CRABP1. We suggest GFAP,RBP3,CRABP1,CRYAAA,APOA1 and SAG as prospective targets that could further be explored as potential candidates in therapy and may further assist in studying the disease mechanism.

SIGNIFICANCE

In this study we evaluated tumor tissue specimens from retinoblastoma patients and identified 39 differentially regulated proteins compared to healthy retina. From these, we propose RBP3, CRABP1, GFAP, CRYAA, APOA1 and SAG as promising proteomic signatures that could further be explored as efficient prognostic and therapeutic targets in retinoblastoma. The present study is not only a contribution to the ongoing endeavour for the discovery of proteomic signatures in retinoblastoma, but, may also act as a starting point for future studies aimed at uncovering novel targets for further therapeutic interventions and improving patient outcomes.

HPV-16 Detected in One-Fourth Eyes With Retinoblastoma: A Prospective Case-control Study From North India

The incidence of nonfamilial retinoblastoma (RB) is believed to be higher in developing countries. The reports on association of human papillomavirus (HPV) with RB are limited and contradictory. The aim was to investigate the prevalence of HPV in RB tumor tissue. In the prospective study, consecutive eyes enucleated for RB from patients lacking a family history of RB were enrolled as cases over a 3-year period. Controls included donor eyes obtained from the eye bank. Normal retinal tissue from the donor eyes and tumor tissue from eyes with RB was subjected to DNA isolation. Polymerase chain reaction followed by dot-blot hybridization was performed to detect 21 HPV genotypes. The study cohort included 39 RB and 42 normal retinal tissues. A positive result for HPV-polymerase chain reaction was obtained in 10 (25.6%) tumor tissues and none of the control eyes. HPV-16 was the only subtype detected. Socioeconomic status (P=0.58) or maternal age (P=0.58) was not associated with presence of HPV. All HPV-positive patients had undergone a vaginal delivery (P=0.60). HPV-16 was detected in one-fourth cases of nonfamilial RB. None of the control cases (donor eyes) tested positive. Implication of the presence of HPV in RB tissue and role in carcinogenesis needs further elucidation.

Human papilloma virus in retinoblastoma tissues from Korean patients

Purpose

Recent reports suggest the association of human papilloma virus (HPV) with retinoblastoma. This study was performed to elucidate whether HPV infection is related to retinoblastoma among Koreans.

Methods

A total of 54 cases diagnosed with retinoblastoma were enrolled from Seoul National University Children's Hospital and Seoul Metropolitan Government-Seoul National University Boramae Medical Center. Presence of human papilloma viral DNA was detected by in situ hybridization in formalin-fixed paraffin-embedded retinoblastoma tissues using both probes against high- and low risk HPV types.

Results

The mean age at diagnosis was 22.0 months (range, 1.1 to 98.0 months), and the mean age at enucleation was 27.8 months (range, 1.5 to 112.7 months) among the 54 patients with retinoblastoma. HPV was not detected in any of the retinoblastoma samples using either high risk or low risk HPV probes.

Conclusions

Our study, being the first study in the Korean population, proposes that HPV infection may have no causal relationship with retinoblastoma in Koreans.

Maternal transmission of human papillomavirus in retinoblastoma: A possible route of transfer

Context:

After establishing the presence of human papillomavirus (HPV) in retinoblastoma (RB), the probable role of the mother was investigated.

Materials and Methods:

A total of 21 sporadic RB cases and 15/21 corresponding mothers′ cervical brushings were collected. HPV testing was carried out using multiplex PCR (PGMY09/11 primers) followed by genotyping using line blot assay.

Results:

We found both high- (83%) and intermediate-risk (17%) HPV types in 12/21 (57%) RB samples and only high-risk (100%) types in 6/15 (40%) cervical brushing samples. The single genotype of HPV 16 was found in six cases and HPVs 82, 68 and 35 in one case each. Both HPVs 16 and 59 were found in two cases and HPV 16 and 73 in one case. Three samples of RB harboring HPV 16, HPVs 16 and 59, and HPVs 16 and 73 had HPV genotype 16 in the respective mothers′ cervical brushing samples.

Conclusions:

Maternal transfer of HPV in RB could be a possible route of transmission. However, a larger cohort and sampling of the mothers′ cervical brushings at various stages, i.e. before, during, and after pregnancy will give us insight to propound an alternate mechanism for the development of sporadic RB.

Perinatal characteristics and retinoblastoma

PURPOSE

The etiology of retinoblastoma remains poorly understood. In the present study, we examined associations between perinatal factors and retinoblastoma risk in California children.

METHODS

We identified 609 retinoblastoma cases (420 unilateral, 187 bilateral, and 2 with laterality unknown) from California Cancer Registry records of diagnoses 1988-2007 among children < 6 years of age. We randomly selected 209,051 controls from California birth rolls. The source of most study data was birth certificates. Multivariable logistic regression was used to examine associations between retinoblastoma and perinatal characteristics.

RESULTS

Bilateral retinoblastoma was associated with greater paternal age [for fathers over 35, crude odds ratio (OR) = 1.73, 95 % confidence interval (CI) 1.20, 2.47] and with twin births (OR = 1.93, 95 % CI 0.99, 3.79). Among unilateral cases, we observed an increased risk among children of US-born Hispanic mothers (OR = 1.34, 95 % CI 1.01, 1.77) while a decreased risk was observed for infants born to mothers with less than 9 years of education (OR = 0.70, 95 % CI 0.49, 1.00), a group that consisted primarily of mothers born in Mexico. We observed that maternal infection in pregnancy with any STD (OR = 3.59, 95 % CI 1.58, 8.15) was associated with bilateral retinoblastoma.

CONCLUSIONS

This study supports the findings of previous investigations reporting associations between parental age, HPV infection, and retinoblastoma.

Viral perturbations of host networks reflect disease etiology

Many human diseases, arising from mutations of disease susceptibility genes (genetic diseases), are also associated with viral infections (virally implicated diseases), either in a directly causal manner or by indirect associations. Here we examine whether viral perturbations of host interactome may underlie such virally implicated disease relationships. Using as models two different human viruses, Epstein-Barr virus (EBV) and human papillomavirus (HPV), we find that host targets of viral proteins reside in network proximity to products of disease susceptibility genes. Expression changes in virally implicated disease tissues and comorbidity patterns cluster significantly in the network vicinity of viral targets. The topological proximity found between cellular targets of viral proteins and disease genes was exploited to uncover a novel pathway linking HPV to Fanconi anemia.

Retinoblastoma major review with updates on Middle East management protocols

Many advances in the field of management of retinoblastoma emerged in the past few years. Patterns of presentation of retinoblastoma in the Middle East region differ from Western community. The use of enucleation as a radical method of eradicating advanced disease is not easily accepted by patient's family. We still do see stage E, failed or resistant retinoblastoma and advanced extraocular disease ensues as a result of delayed enucleation decision. In this review, we discuss updates in management of retinoblastoma with its implication on patients in our part of the world. Identifying clinical and high risk characteristics is important prognostically and are discussed for further management of retinoblastoma cases.

Evidence for the presence of high risk human papillomavirus in retinoblastoma tissue from nonfamilial retinoblastoma in developing countries

BACKGROUND

The prevalence of human papillomavirus (HPV) infection in India is high. HPV infection is known to cause cervical cancer and has also been implicated in the pathogenesis of retinoblastoma (RB), a common intraocular malignant tumor of childhood which can be familial or sporadic. Despite the high incidence of RB in India, its familial form is rare. Hence this study was undertaken to investigate whether high-risk HPV types 16 and 18 are involved in the development of RB.

METHODS

Formalin fixed paraffin embedded RB tissues (n = 76) including prospective cases with corresponding maternal cervical smears (n = 10) were analyzed for the presence of HPV DNA sequences. Expression of the cell cycle regulatory proteins viz; p105, p107, p30, p16, E2F-1, E2F-4, and MiB-1 was studied by immunohistochemistry (IHC) (n = 34).

RESULTS

A total of 53 out of 76 (69.7%) cases were positive for HPV, of these 3 cases were positive for HPV-16, 23 for HPV-18, and 27 for both HPV-16 and -18. Of the prospective cases (n = 10) studied, five cases along with the corresponding maternal cervical cytology smear had identical HPV status. HPV-16 positive tumors were classified as well differentiated (P = 0.013). Nuclear expression of pRB2/p130 showed significant association with HPV-16 infection (P = 0.04) or dual infection of HPV-16/-18 (P = 0.02).

CONCLUSIONS

Our study lends support to the hypothesis that infection of HPV-16/-18 may play an important role in the development of nonfamilial form of RB in children in India.

Retinoblastoma: Recent trends A mini review based on published literature

Retinoblastoma (RB) is the most common intraocular malignancy in children. Recently, there have been significant advances made in the molecular pathology and the management of the disease. Last decade has witnessed better understanding of the genetics of RB, the discovery of new tumor markers expressed by the RB tumors, the identification of high-risk histopathological factors following enucleation, and newer methods of treatment including periocular chemotherapy and superselective intraarterial chemotherapy. All these advances have translated in improved survival rates for the affected children, improved rates of eye salvage, and improved visual outcomes. This article briefly reviews these advances.Method of Literature Search: Literature on the Medline database was searched using the PubMed interface. The search strategy included MeSH and natural language terms using the keywords mentioned. Reference lists in retrieved articles and textbooks were also searched for relevant references.

Molecular pathology of retinoblastoma

Retinoblastoma (RB) is an embryonic neoplasm of retinal origin. For many years, scientists have sought the fundamental origins of tumorigenesis, with the ultimate hope of discovering a cure. Indeed, these efforts have led to a significant understanding that multiple molecular and genetic aberrations, such as uncontrolled proliferation and the inhibition of apoptosis that contribute to the canonical characteristics of tumor biology. Despite these advances, a thorough understanding, such as the precise cells, which are the targets of neoplastic transformation, especially in solid tumors, is currently lacking. The focus of this review is to emphasize the molecular defects involved in the RB tumor progression and mechanisms associated with inhibition of tumor cell apoptotic processes. This review also discusses the importance of target molecules characterization and their potential therapeutic or prognostic use in RB disease.

Socioeconomic status and the incidence of non-central nervous system childhood embryonic tumours in Brazil

Background

Childhood cancer differs from most common adult cancers, suggesting a distinct aetiology for some types of childhood cancer. Our objective in this study was to test the difference in incidence rates of 4 non-CNS embryonic tumours and their correlation with socioeconomic status (SES) in Brazil.

Methods

Data was obtained from 13 Brazilian population-based cancer registries (PBCRs) of neuroblastoma (NB), Wilms'tumour (WT), retinoblastoma (RB), and hepatoblastoma (HB). Incidence rates by tumour type, age, and gender were calculated per one million children. Correlations between social exclusion index (SEI) as an indicator of socioeconomic status (SES) and incidence rates was investigated using the Spearman's test.

Results

WT, RB, and HB presented with the highest age-adjusted incidence rates (AAIRs) in 1 to 4 year old of both genders, whereas NB presented the highest AAIR in ≤11 month-olds. However, differences in the incidence rates among PBCRs were observed. Higher incidence rates were found for WT and RB, whereas lower incidence rates were observed for NB. Higher SEI was correlated with higher incidences of NB (0.731; p = 0.0117), whereas no SEI correlation was observed between incidence rates for WT, RB, and HB. In two Brazilian cities, the incidence rates of NB and RB were directly correlated with SEI; NB had the highest incidence rates (14.2, 95% CI, 8.6-19.7), and RB the lowest (3.5, 95% CI, 0.7-6.3) in Curitiba (SEI, 0.730). In Natal (SEI, 0.595), we observed just the opposite; the highest incidence rate was for RB and the lowest was for NB (4.6, 95% CI, 0.1-9.1).

Conclusion

Regional variations of SES and the incidence of embryonal tumours were observed, particularly incidence rates for NB and RB. Further studies are necessary to investigate risk factors for embryonic tumours in Brazil.

Low prevalence of HPV in Brazilian children with retinoblastoma

Retinoblastoma is the most frequent intra-ocular malignant tumor of the childhood, occurring in 1 of 18,000-30,000 live births. Little is known about the causes of sporadic retinoblastoma and only a few authors have investigated the etiologic role of human papillomavirus (HPV), with controversial results. Formalin-fixed, paraffin-embedded tissue blocks containing retinoblastoma were retrieved from the archives of the Department of Pathology at Hospital A C Camargo, São Paulo, Brazil. All patients were treated with enucleation (21 children had both eyes enucleated). Retinoblastoma and, when possible, normal retina of each specimen, were micro-dissected under direct light microscopic visualization by using a PixCell II Laser Capture Micro-dissection System. The DNA quality was evaluated by polymerase chain reaction (PCR) amplification of 110 base pairs fragment of the human β-globin gene using primers PCO3+/PCO4+. All globin positive specimens were analyzed by PCR for the presence of HPV DNA using consensus primers GP5+/GP6+. A total of 154 specimens were evaluated. Forty-four patients also had normal retinal specimens available for analysis of DNA HPV. The DNA HPV prevalence among all tumor specimens was 4.6% (95% CI 2.0; 8.8) (7 positive specimens/153 adequate specimens). Among normal retinal specimens, the DNA HPV prevalence was 9.1% (95% CI 2.9; 20.5) (4 positive specimens/44 specimens). There was no statistically significant difference between these rates (P = 0.318). Excluding any experimental failure, our results indicate a low prevalence of HPV DNA in retinoblastomas. We were therefore unable to conclude about the association between these oncogenic viruses and this rare pediatric neoplasm.

Recent advances in retinoblastoma genetic research

PURPOSE OF REVIEW

Retinoblastoma is a pediatric eye tumor that serves as a paradigm for understanding the genetic basis of cancer. This review will highlight recent advances in retinoblastoma genetic research and discuss how these new findings influence our knowledge of retinoblastoma tumorigenesis and management.

RECENT FINDINGS

Current data demonstrate that retinomas, benign retinal tumors found in some retinoblastoma patients, exhibit bi-allelic mutations in RB1, the retinoblastoma gene, and lack of expression of the retinoblastoma protein. Interestingly, retinomas demonstrate a low level of genomic instability that becomes progressively more severe in retinoblastoma tumors. Additionally, a subset of retinomas share genomic alterations with retinoblastoma. Collectively, these data suggest that retinomas represent true premalignant lesions and not regressed retinoblastoma tumors, as previously thought. Translational advances in retinoblastoma genetic research include development of an allele-specific assay that now enables the identification of mutational mosaicism, thereby increasing the rate of RB1 mutation detection in bilaterally affected patients to as high as 95%.

SUMMARY

These and related research efforts reveal novel data that enhance our understanding of the biology of retinoblastoma. These observations may facilitate new therapeutic approaches to further decrease the morbidity and mortality associated with retinoblastoma and other more common forms of cancer.