The genetics of retinoblastoma

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.

Childhood cancer incidence rates and hazardous air pollutants in California: an exploratory analysis

Hazardous air pollutants (HAPs) are compounds shown to cause cancer or other adverse health effects. We analyzed population-based childhood cancer incidence rates in California (USA) from 1988 to 1994, by HAP exposure scores, for all California census tracts. For each census tract, we calculated exposure scores by combining cancer potency factors with outdoor HAP concentrations modeled by the U.S. Environmental Protection Agency. We evaluated the relationship between childhood cancer rates and exposure scores for 25 potentially carcinogenic HAPs emitted from mobile, area, and point sources and from all sources combined. Our study period saw 7,143 newly diagnosed cancer cases in California; of these, 6,989 (97.8%) could be assigned to census tracts and included in our analysis. Using Poisson regression, we estimated rate ratios (RRs) adjusted for age, race/ethnicity, and sex. We found little evidence for elevated cancer RRs for all sites or for gliomas among children living in high-ranking combined-source exposure areas. We found elevated RRs and a significant trend with increasing exposure level for childhood leukemia in tracts ranked highest for exposure to the combined group of 25 HAPs (RR = 1.21; 95% confidence interval, 1.03, 1.42) and in tracts ranked highest for point-source HAP exposure (RR = 1.32; 95% confidence interval, 1.11, 1.57). Our findings suggest an association between increased childhood leukemia rates and high HAP exposure, but studies involving more comprehensive exposure assessment and individual-level exposure data will be important for elucidating this relationship.

Childhood cancer and agricultural pesticide use: an ecologic study in California

We analyzed population-based childhood cancer incidence rates throughout California in relation to agricultural pesticide use. During 1988-1994, a total of 7,143 cases of invasive cancer were diagnosed among children under 15 years of age in California. Building on the availability of high-quality population-based cancer incidence information from the California Cancer Registry, population data from the U.S. Census, and uniquely comprehensive agricultural pesticide use information from California's Department of Pesticide Regulation, we used a geographic information system to assign summary population, exposure, and outcome attributes at the block group level. We used Poisson regression to estimate rate ratios (RRs) by pesticide use density adjusted for race/ethnicity, age, and sex for all types of childhood cancer combined and separately for the leukemias and central nervous system cancers. We generally found no association between pesticide use density and childhood cancer incidence rates. The RR for all cancers was 0.95 [95% confidence interval (CI), 0.80-1.13] for block groups in the 90th percentile and above for use of pesticides classified as probable carcinogens, compared to the block groups with use of < 1 lb/mi(2). The RRs were similar for leukemia and central nervous system cancers. Childhood leukemia rates were significantly elevated (RR = 1.48; 95% CI, 1.03-2.13) in block groups with the highest use of propargite, although we saw no dose-response trend with increasing exposure categories. Results were unchanged by further adjustment for socioeconomic status and urbanization.

Retinoblastoma: problems and perspectives from India

This study examined the salient clinical and epidemiological characteristics of retinoblastoma (RB) in India, thereby highlighting the problems encountered there. The epidemiological characteristics of 296 patients with RB over 8 years were evaluated using hospital records and postal follow-ups. Unilateral disease was seen in 61.8% of patients. The overall median age at presentation was 3.5 years (3.5 years for unilateral RB and 1.0 years for bilateral RB). The male/female ratio was 1.4:1. The median duration of symptomatic disease was 8 months. Consanguineous marriage was seen in 17% and family history of RB was noted in 1.7% cases. Also, 2% had a history of other malignancy in the family. Associated congenital malformation was seen in 10.5% of cases. A second malignancy was seen in 0.67% of cases at a mean duration of 4.5 years after completion of therapy. A predominance of advanced-stage disease (74.5% had Reese-Ellsworth group IV and V disease) was seen in our series. Only 43.6% of patients had disease localized to the globe without any infiltration/invasion. The majority of cases had advanced-stage disease at presentation and came from the underprivileged class of society. Patients with bilateral RB presented much earlier than those with unilateral disease. In patients with unilateral RB, higher age at presentation as well as advanced disease may be related to much delay in seeking medical attention. In view of the advanced stage at presentation, there also exist a possibility of difference in the biology of the tumor seen in these patients.

[Evaluation of cancer risk through genetic analysis?]

BACKGROUND

The recent literature of familial cancer, specifically related to germline mutations of RB1, p53, NF1, ATM, BRCA1, Mismatch repair genes and APC is reviewed.

RESULTS AND CONCLUSIONS

Germline mutations do not relate to an increased tumor risk of any single tissue, but instead to spectra of neoplastic diseases. The genetic background plays a major role in modifying the cancer risk. Therefore, mass screening for mutations of single genes seems to be without practical value. Only in combination with an adequate and informative family history can molecular genetic analysis significantly support the care for the individual. Comparison of the data of patients inheriting germline mutations and the experience from the corresponding "knockout" mouse demonstrate that only the p53 and APC knockout mice are useful models of human disease.

Survival after retinoblastoma: long-term consequences and family history of cancer

Retinoblastoma (Rb) is a rare childhood tumor of the eye. In the heritable form, tumors are often bilateral and survivors have a greatly increased risk both for a second malignancy and for having children with Rb. Familial patterns of both cancer and birth defects are poorly understood in families with a heritable cancer, and little is known of the ways that a heritable cancer affects the lives of long-term survivors. To find out more about these and other issues in the lives of long-term survivors of childhood and adolescent cancer, we interviewed 56 adult survivors of retinoblastoma (15 with the heritable form) and 84 brothers and sisters as controls, who formed part of a large retrospective cohort study. Rb survivors were interviewed between 1980 and 1983, when they were 30 years old on average. Types of employment and health problems did not differ between survivors and controls, regardless of sight, but the income of blind survivors was considerably less than that of partially sighted survivors. Despite similar marriage rates, fewer survivors than controls reported a pregnancy (RR = 0.45; 95% CI; 0.24-0.83 for both sexes combined). Parents of children with heritable Rb seemed more likely to have had cancer than parents in families with nonheritable Rb (P = 0.06), and mothers were more likely than fathers to be affected (P = 0.01). This small series suggests that having retinoblastoma may have many long-term consequences, reaching beyond genetic and physical effects to touch family life and income attainment and the health of other family members. Follow-up of more modern cohorts and the use of molecular tools will clarify the long-term consequences of more recent therapies, and patterns of familiar cancer.

Malformations in children with soft tissue sarcoma and in their parents and siblings

The presence of malformations in a population-based series of 181 children diagnosed with soft tissue sarcoma and in the majority of their parents and siblings was ascertained from family interviews and medical records. Five index children (2.8%) had serious anomalies, a figure not in excess of that derived from general population data. Fourteen siblings (4%) were affected, and higher rates of malformations were seen in siblings of female case children (P = 0.06) and siblings of children with visceral tumours (P = 0.03). There was no correlation between site of tumour in the index and specific organ system anomalies in the index or in their respective siblings. The survey indicated that there are unlikely to be strong associations between childhood soft tissue sarcoma and major malformations, a situation distinct from that found in Wilms' tumour.

Competing stochastic models of the incubation period: an investigation of age-at-diagnosis of familial and sporadic retinoblastoma

This study is based on the assumption that the distribution of age-at-diagnosis (a synonym for the incubation period) of a disease can convey information with respect to its pathogenetic mechanisms. To this end, an analysis of 3 retinoblastoma (RB) international data sets was undertaken. The molecular and cellular basis of RB is well understood and may serve our purpose well. RB is broken down into familial bilateral, unilateral, and sporadic unilateral forms. Survival and hazard functions were computed. Several competing stochastic models (up to 9 per RB form) were fit. Each conveyed a meaningful pathogenetic mechanism. Between-model discrimination was achieved by examining chi-square goodness-of-fit values to select the best fitting model. Well-known survival models, such as the simple exponential and the lognormal (Sartwell model) were ruled out. Age-at-diagnosis of familial RB proved to be best explained by 2 interfering exponentials (a diffonential function); the logistic was retained as the best adjusted model of the incubation period of sporadic cases of RB. As to familial unilaterals, both the diffonential and the logistic models fit equally well. The 3 data sets are consistent in these results, ruling out the less well-fit competing models. The results suggest the existence of 2 opposing but independent balancing internal mechanisms at the origin of familial RB. Sporadic RB appears to be due to a single host-dependent self-limiting cellular mechanism. Familial unilaterals which share both of these component mechanisms would involve a lower retinoblast turnover rate. The cellular implications of these findings are discussed with regard to the relative importance of endogenous and exogenous induction factors in RB. It is concluded that, according to the RB form, RB occurrence results from 2 cellular interfering forces of different strength and organization.

Oncology

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Low frequency of retinoblastoma gene alterations in rat hepatocellular carcinomas

Abnormalities of the retinoblastoma (Rb) gene have been reported in some human cancers, including hepatocellular carcinomas (HCCs). We examined by Southern blotting the status of the Rb gene in HCCs induced in rats in four experimental models. A low frequency of Rb gene alterations, detected as novel hybridizing bands unique to each tumor, was observed. Expression of the Rb protein product was examined in the HCCs and in seven established rat hepatoma cell lines studied. It appears, therefore, that alterations in the structure or expression of the Rb gene do occur but probably do not contribute in a major way to hepatocarcinogenesis in the rat.

Patterns of risk of hereditary retinoblastoma and applications to genetic counselling

A registry including information about nearly 1,600 cases of retinoblastoma diagnosed in Britain has been created at the Childhood Cancer Research Group. Cases have been classified as 'old germ cell mutation', 'new germ cell mutation' or 'sporadic non-hereditary'. For a population-based group of 918 cases diagnosed between 1962 and 1985 we have calculated the proportions of unilateral/bilateral and hereditary/non-hereditary cases. Bilateral cases represent 40% of the total number over this period; the proportion known to be hereditary is 44%, a higher proportion than has been reported elsewhere. By following up selected groups of cases, an estimate has been made of the proportions of siblings of retinoblastoma patients and offspring of survivors from retinoblastoma who are themselves affected with the disease. Where there is no previous family history, the risk for siblings of retinoblastoma patients of developing the disease is approximately 2% if the disease in the affected child is bilateral and 1% if it is unilateral, assuming that there are no other siblings; if there are unaffected siblings the risks for subsequent children are lower. Children of patients with hereditary retinoblastoma have a one in two chance of carrying the germ cell mutation and for those who are carriers the probability of developing retinoblastoma is very close to the accepted figure of 90% if the parents have bilateral retinoblastoma but probably less if they have the unilateral form. For children of patients not known to be carriers, the probability of developing retinoblastoma is estimated to be about 1%, considerably lower than the previously accepted figure of about 5%. Retinoblastoma kindreds consist mainly of bilateral cases but there is evidence that some kindreds have a high proportion of unilateral cases. The ways in which these findings may be used in conjunction with modern techniques of molecular biology for prenatal and postnatal genetic counselling are discussed.

Chromosome studies of solid tumours

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Follow-up of retinoblastoma patients having prenatal and perinatal predictions for mutant gene carrier status using intragenic polymorphic probes from the RB1 gene

We have carried out presymptomatic prediction of mutant gene carrier status in ten individuals with a family history of retinoblastoma. In all cases standard linkage studies were employed using intragenic DNA probes which recognise restriction fragment length polymorphisms. In four cases foetal DNA samples were obtained by chorionic villus sampling, the remaining six were derived from either cord blood samples or venipuncture of neonates. We demonstrated that the mutant gene was inherited by only one of these patients who has subsequently developed bilateral tumours. Six of the other cases have now reached the age beyond which it might have been expected that tumours would develop and are all disease free. It must be concluded that repeated ophthalmological examination of these and future patients shown not to have inherited the mutant gene, is unnecessary.