Two genetic hits (more or less) to cancer

Most cancers have many chromosomal abnormalities, both in number and in structure, whereas some show only a single aberration. In the era before molecular biology, cancer researchers, studying both human and animal cancers, proposed that a small number of events was needed for carcinogenesis. Evidence from the recent molecular era also indicates that cancers can arise from small numbers of events that affect common cell birth and death processes.

Retinoblastoma

Retinoblastoma is an aggressive eye cancer of infancy and childhood. Survival and the chance of saving vision depend on severity of disease at presentation. Retinoblastoma was the first tumour to draw attention to the genetic aetiology of cancer. Despite good understanding of its aetiology, mortality from retinoblastoma is about 70% in countries of low and middle income, where most affected children live. Poor public and medical awareness, and an absence of rigorous clinical trials to assess innovative treatments impede progress. Worldwide, most of the estimated 9000 newly diagnosed patients every year will die. However, global digital communications present opportunities to optimise standards of care for children and families affected by this rare and often devastating cancer. Parents are now leading the effort for widespread awareness of the danger of leucocoria. Genome-level technologies could make genetic testing a reality for every family affected by retinoblastoma. Best-practice guidelines, online sharing of pathological images, point-of-care data entry, multidisciplinary research, and clinical trials can reduce mortality. Most importantly, active participation of survivors and families will ensure that the whole wellbeing of the child is prioritised in any treatment plan.

The international incidence of childhood cancer

The International Agency for Research on Cancer has coordinated a worldwide study of the incidence of cancer in childhood. Contributors from over 50 countries have provided data. This paper presents a summary of some of the major results. The incidence rates and relative frequencies of childhood cancers are described according to 12 diagnostic groups, defined mainly in terms of tumour morphology. Variations in the risk of those tumours between different countries and different ethnic groups provide important information on the relative importance of environmental and genetic factors in their aetiology.

Incidence of second primary tumours among childhood cancer survivors

Among a cohort of 10,106 three-year survivors of childhood cancer, 90 second primary tumours (SPTs) were observed. Within 25 years of 3-year survival about 4% developed a SPT, about 6-fold expected, the relative risk not varying much with increasing follow-up. Following genetic retinoblastoma we observed 30-fold the expected number of SPTs, and over 400-fold the expected number of osteosarcomas. The risk of SPT in the absence of radiotherapy and chemotherapy (inherent risk) following genetic retinoblastoma was 13-fold expected and over 200-fold the expected number of osteosarcomas were observed. There was evidence that both radiotherapy and cyclophosphamide were associated with an increased risk of SPT. After all first primary tumours (FPTs) excluding retinoblastoma we observed almost 5-fold the expected number of SPTs. The inherent risk was 4-fold expected, the relative risks associated with radiotherapy but no chemotherapy, and both radiotherapy and chemotherapy were 6- and 9-fold expected respectively. There were about 20-fold the number of malignant bone tumours expected, most were osteosarcoma; also 7-fold the number of central nervous system tumours expected. There were 8 basal cell carcinomas and it seems likely that radiotherapy was involved in the development of some of these. Radiotherapy appears to have been involved in the development of many of the SPTs observed following all FPTs excluding retinoblastoma, particularly after CNS tumours, Wilms' tumour and Hodgkin's disease. Currently there is insufficient follow-up to examine the risk following chemotherapy. After acute leukaemia there was 20-fold the expected number of central nervous system tumours, though this is based on only 3 cases; whether therapy is directly involved in their development is uncertain. The risks we report are rarely greater than those reported in previous large-scale studies; in most instances they are substantially less. It is very unlikely that many SPTs were missed with our follow-up system so alternative explanations require further investigation; in particular it is possible the lower risks in our data compared to series treated in the United States may be explained, in part, by less combination therapy and lower doses of radiotherapy.

Epigenetics and assisted reproductive technology: a call for investigation

A surprising set of recent observations suggests a link between assisted reproductive technology (ART) and epigenetic errors--that is, errors involving information other than DNA sequence that is heritable during cell division. An apparent association with ART was found in registries of children with Beckwith-Wiedemann syndrome, Angelman syndrome, and retinoblastoma. Here, we review the epidemiology and molecular biology behind these studies and those of relevant model systems, and we highlight the need for investigation of two major questions: (1) large-scale case-control studies of ART outcomes, including long-term assessment of the incidence of birth defects and cancer, and (2) investigation of the relationship between epigenetic errors in both offspring and parents, the specific methods of ART used, and the underlying infertility diagnoses. In addition, the components of proprietary commercial media used in ART procedures must be fully and publicly disclosed, so that factors such as methionine content can be assessed, given the relationship in animal studies between methionine exposure and epigenetic changes.

Global Retinoblastoma Presentation and Analysis by National Income Level

Importance

Early diagnosis of retinoblastoma, the most common intraocular cancer, can save both a child's life and vision. However, anecdotal evidence suggests that many children across the world are diagnosed late. To our knowledge, the clinical presentation of retinoblastoma has never been assessed on a global scale.

Objectives

To report the retinoblastoma stage at diagnosis in patients across the world during a single year, to investigate associations between clinical variables and national income level, and to investigate risk factors for advanced disease at diagnosis.

Design, Setting, and Participants

A total of 278 retinoblastoma treatment centers were recruited from June 2017 through December 2018 to participate in a cross-sectional analysis of treatment-naive patients with retinoblastoma who were diagnosed in 2017.

Main Outcomes and Measures

Age at presentation, proportion of familial history of retinoblastoma, and tumor stage and metastasis.

Results

The cohort included 4351 new patients from 153 countries; the median age at diagnosis was 30.5 (interquartile range, 18.3-45.9) months, and 1976 patients (45.4%) were female. Most patients (n = 3685 [84.7%]) were from low- and middle-income countries (LMICs). Globally, the most common indication for referral was leukocoria (n = 2638 [62.8%]), followed by strabismus (n = 429 [10.2%]) and proptosis (n = 309 [7.4%]). Patients from high-income countries (HICs) were diagnosed at a median age of 14.1 months, with 656 of 666 (98.5%) patients having intraocular retinoblastoma and 2 (0.3%) having metastasis. Patients from low-income countries were diagnosed at a median age of 30.5 months, with 256 of 521 (49.1%) having extraocular retinoblastoma and 94 of 498 (18.9%) having metastasis. Lower national income level was associated with older presentation age, higher proportion of locally advanced disease and distant metastasis, and smaller proportion of familial history of retinoblastoma. Advanced disease at diagnosis was more common in LMICs even after adjusting for age (odds ratio for low-income countries vs upper-middle-income countries and HICs, 17.92 [95% CI, 12.94-24.80], and for lower-middle-income countries vs upper-middle-income countries and HICs, 5.74 [95% CI, 4.30-7.68]).

Conclusions and Relevance

This study is estimated to have included more than half of all new retinoblastoma cases worldwide in 2017. Children from LMICs, where the main global retinoblastoma burden lies, presented at an older age with more advanced disease and demonstrated a smaller proportion of familial history of retinoblastoma, likely because many do not reach a childbearing age. Given that retinoblastoma is curable, these data are concerning and mandate intervention at national and international levels. Further studies are needed to investigate factors, other than age at presentation, that may be associated with advanced disease in LMICs.

Infant cancer in the U.S.: histology-specific incidence and trends, 1973 to 1992

BACKGROUND

Many cancers in infants demonstrate unique epidemiologic, clinical, and genetic characteristics compared with cancers in older children. Few epidemiologic reports, however, have focused on this important age group.

METHODS

Population-based data from the Surveillance, Epidemiology, and End Results (SEER) program were used to estimate relative frequency, incidence rates, and average annual percentage change of rates among children in their first year of life (infants) who were diagnosed with a malignant neoplasm from 1973 to 1992 (N = 1461).

RESULTS

The greatest proportion of cases (12%) was diagnosed during the first month of life, with extracranial neuroblastoma accounting for 35% of this total. Overall, the average annual incidence rate was 223/1,000,000 infants. Extracranial neuroblastoma was the most common infant malignancy (58/1,000,000 infants per year), followed by leukemias (37/1,000,000), brain and central nervous system (CNS) tumors (34/1,000,000), and retinoblastoma (27/1,000,000). White infants had a 32% higher incidence rate than black infants. The average annual percentage increase in rates for all cancer from 1973 to 1992 was 2.9% (95% CI: 1.9%, 3.8%). For neoplasms with at least 100 cases, increasing trends were greatest for retinoblastoma (4.6%), CNS (4.1%), and extracranial neuroblastoma (3.4%).

CONCLUSIONS

Incidence rates increased notably over the study period. Future studies should consider the unique presentation of infants with cancer when developing new hypotheses related to cancer etiology and gene-environment interactions.

Incidence of retinoblastoma in children born after in-vitro fertilisation

Every year, 3000 women in the Netherlands are treated with in-vitro fertilisation (IVF), and results from studies suggest that the offspring of these women do not have a heightened risk of cancer. Between November, 2000, and February, 2002, we diagnosed retinoblastoma in five patients born after IVF. To calculate the relative risk of the disease, we assumed that the proportion of children conceived by IVF in the Netherlands is between 1.0 and 1.5%, and that the five patients who we diagnosed with the disease represent all new cases in the Netherlands during that period. Relative risks for retinoblastoma were significantly raised (7.2 [95% CI 2.4-17.0], and 4.9 [1.6-11.3], for 1% and 1.5% rates, respectively). This possible association of an increased risk of retinoblastoma in a population-based study needs to be established.

Imprinting diseases and IVF: Danish National IVF cohort study

BACKGROUND

The aim of this study was to compare the frequency of imprinting diseases in children born after IVF with the incidence in naturally conceived children.

METHODS

All singleton children born in Denmark from January 1, 1995 through December 31, 2001 were stratified into children born without and after IVF, and were followed from birth until the end of 2002 in the National Register of Patients and the Central Register of Psychiatric Diseases, which include all discharge diagnoses from somatic and psychiatric hospitals/clinics, respectively. Included in the study were malignancies, mental, behavioural and neurological diseases, congenital syndromes, and developmental disturbances. Only diagnosis codes potentially relevant for imprinting diseases were included.

RESULTS

During the 7-year study period, 442,349 singleton non-IVF and 6052 IVF children were born. Mean follow-up time was 4.5 and 4.1 years for the two groups, respectively, corresponding to 2 million and 25 000 follow-up years. In the IVF/non-IVF cohort, we detected 0/72 children with cancer, 47/3766 with mental diseases, 72/3654 neurological diseases, 4/287 congenital syndromes and 96/6727 developmental disturbances, in a total of 219/14,506 clinical outcomes. The number of children with specific imprinting diseases in the non-IVF group was 54: 44 kidney cancers, five retinoblastoma, three Prader-Willi syndrome and two Russel-Silver syndrome. Anticipating the same occurrence in IVF children, the total expected number was calculated to be 0.74. The observed number in the IVF group was 0. We found a significantly increased risk of cerebral palsy in the IVF group, with a rate ratio (RR) (IVF:non-IVF) of 1.8 [95% confidence interval (CI) 1.2-2.8; P < 0.01], and of sleeping disturbances, with an RR 2.0 (95% CI 1.2-3.3). The incidence rate of childhood cancers, mental diseases, congenital syndromes and developmental disturbances was equal in the two groups.

CONCLUSIONS

We found no indication of an increased risk of imprinting diseases after IVF, but an 80% increased risk of cerebral palsy. We observed equal frequencies of childhood cancers, mental diseases, congenital syndromes and developmental disturbances in the two groups. Danish register data do not support reports of an increased risk of imprinting diseases after IVF.

Case-control study of parental age, parity and socioeconomic level in relation to childhood cancers

BACKGROUND

Parental ages, parity, and social class have been found in some studies to be associated with particular childhood cancers. Further investigation is warranted because of conflicting findings, biases, and the need to test specific hypotheses.

METHODS

A case-control study was conducted (England and Wales, ages 0-14 years). Cases were ascertained from the National Registry of Childhood Tumours, and were born and diagnosed during 1968-1986. Birth record controls were matched 1:1 to cases on date of birth, sex and area. Information on variables of interest for both groups came from birth records. In all, 10 162 pairs could contribute to matched analyses.

RESULTS

The odds ratio (OR) for retinoblastoma resulting from assumed new germ cell mutations among children of fathers aged > or =45 years was 3.0 (95% CI : 0.2-41.7). The risk of childhood acute lymphoblastic leukaemia (ALL) was significantly higher among children of older mothers and fathers, and significant trends with increasing mothers' (P < 0.001) and fathers' (P = 0.002) ages were found. There was a strong and significant protective effect of increasing parity on risk of childhood ALL. The adjusted OR for parity of > or =5 (versus 0) was 0.5 (95% CI : 0.3-0.8). Children in more deprived communities had a lower risk of ALL; but this was not significant after confounders were allowed for. There was no significant effect of social class based on parental occupation on ALL risk, but the numbers were small in those analyses.

CONCLUSIONS

The associations between ALL and parental ages did not disappear when children with Down syndrome were excluded, suggesting an additional explanation beyond known links. The strong ALL association with parity may be because of an unknown environmental risk factor.

Retinoblastoma and Neuroblastoma Predisposition and Surveillance

Retinoblastoma (RB) is the most common intraocular malignancy in childhood. Approximately 40% of retinoblastomas are hereditary and due to germline mutations in the RB1 gene. Children with hereditary RB are also at risk for developing a midline intracranial tumor, most commonly pineoblastoma. We recommend intensive ocular screening for patients with germline RB1 mutations for retinoblastoma as well as neuroimaging for pineoblastoma surveillance. There is an approximately 20% risk of developing second primary cancers among individuals with hereditary RB, higher among those who received radiotherapy for their primary RB tumors. However, there is not yet a clear consensus on what, if any, screening protocol would be most appropriate and effective. Neuroblastoma (NB), an embryonal tumor of the sympathetic nervous system, accounts for 15% of pediatric cancer deaths. Prior studies suggest that about 2% of patients with NB have an underlying genetic predisposition that may have contributed to the development of NB. Germline mutations in ALK and PHOX2B account for most familial NB cases. However, other cancer predisposition syndromes, such as Li-Fraumeni syndrome, RASopathies, and others, may be associated with an increased risk for NB. No established protocols for NB surveillance currently exist. Here, we describe consensus recommendations on hereditary RB and NB from the AACR Childhood Cancer Predisposition Workshop. Clin Cancer Res; 23(13); e98-e106. ©2017 AACRSee all articles in the online-only CCR Pediatric Oncology Series.

Modern treatment of retinoblastoma: A 2020 review

Retinoblastoma management remains complex, requiring individualized treatment based on International Classification of Retinoblastoma (ICRB) staging, germline mutation status, family psychosocial factors and cultural beliefs, and available institutional resources. For this 2020 retinoblastoma review, PubMed was searched for articles dated as early as 1931, with an emphasis on articles from 1990 to the present day, using keywords of retinoblastoma, chemotherapy, intravenous chemotherapy, chemoreduction, intra-arterial chemotherapy, ophthalmic artery chemosurgery, intravitreal chemotherapy, intracameral chemotherapy, cryotherapy, transpupillary thermotherapy, laser, radiation, external beam radiotherapy, plaque radiotherapy, brachytherapy, and enucleation. We discuss current treatment modalities as used in the year 2020, including intravenous chemotherapy (IVC), intra-arterial chemotherapy (IAC), intravitreal chemotherapy (IvitC), intracameral chemotherapy (IcamC), consolidation therapies (cryotherapy and transpupillary thermotherapy [TTT]), radiation-based therapies (external beam radiotherapy [EBRT] and plaque radiotherapy), and enucleation. Additionally, we present a consensus treatment algorithm based on the agreement of three North American retinoblastoma treatment centers, and encourage further collaboration amongst the world's most expert retinoblastoma treatment centers in order to develop consensus management plans and continue advancement in the identification and treatment of this childhood cancer.

Parental age and risk of childhood cancers: a population-based cohort study from Sweden

BACKGROUND

Frequent germ line cells mutations were previously demonstrated to be associated with aging. This suggests a higher incidence of childhood cancer among children of older parents. A population-based cohort study of parental ages and other prenatal risk factors for five main childhood cancers was performed with the use of a linkage between several national-based registries.

METHODS

In total, about 4.3 million children with their parents, born between 1961 and 2000, were included in the study. Multivariate Poisson regression was used to obtain the incidence rate ratios (IRR) and 95% confidence interval (CI). Children <5 years of age and children 5-14 years of age were analysed independently.

RESULTS

There was no significant result for children 5-14 years of age. For children <5 years of age, maternal age were associated with elevated risk of retinoblastoma (oldest age group's IRR = 2.39, 95%CI = 1.17-4.85) and leukaemia (oldest age group's IRR = 1.44, 95%CI = 1.01-2.05). Paternal age was significantly associated with leukaemia (oldest age group's IRR = 1.31, 95%CI = 1.04-1.66). For central nervous system cancer, the effect of paternal age was found to be significant (oldest age group's IRR = 1.69, 95%CI = 1.21-2.35) when maternal age was included in the analysis.

CONCLUSION

Our findings indicate that advanced parental age might be associated with an increased risk of early childhood cancers.

Screening for retinoblastoma: presenting signs as prognosticators of patient and ocular survival

OBJECTIVE

To correlate 3 common presenting signs of retinoblastoma with patient and ocular survival and to assess the efficacy of current pediatric screening practices for retinoblastoma.

METHODS

A retrospective study was conducted of 1831 retinoblastoma patients from our center (1914-June 2000). Patient survival (excluding deaths from other primary neoplasms) and ocular survival (presenting eyes) rates were calculated and analyzed using the Kaplan-Meier method.

RESULTS

Leukocoria correlated with excellent patient survival (>86%, 5 years) but poor ocular survival in unilateral (4%, 5 years) and bilateral patients (29%, 5 years). A total of 308 (19%) of 1654 patients presented with strabismus: patient survival was excellent (90%, 5 years), and ocular survival was poor (17%, 5 years) yet better than leukocoria. Patients who had a family history of retinoblastoma and were clinically screened for retinal tumors from birth were diagnosed younger (8 months of age) and earlier (Reese Ellsworth group 1 = 26 [58%] of 45) and had better ocular survival than nonscreened patients with a family history. More patients were initially detected by family/friends (1315 [80%] of 1632) than pediatricians (123 [8%] of 1632) or ophthalmologists (156 [10%] of 1632).

CONCLUSION

Most US children whose retinoblastoma is diagnosed initially present with leukocoria detected by a parent, despite routine pediatric screening for leukocoria via the red reflex test. Initial disease detection at the point of leukocoria or strabismus correlated with high patient survival rates and poor ocular survival rates for the presenting eye. Saving eyes and vision requires disease recognition before leukocoria, as demonstrated by the better ocular salvage rate among patients who had a positive family history and received clinical surveillance via early, routine dilated funduscopic examinations by an ophthalmologist.

The incidence of retinoblastoma

Data from the Third National Cancer Survey indicate that the annual incidence of retinoblastoma in the United States is 11.0 new cases per million children under the age of 5 years. In response to a reported excess of mortality among blacks, rates were computed by race. There was a rate of 10.8 cases per million children for the whites compared to 9.8 cases per million for the blacks. Among the total of 61 newly diagnosed cases reported among residents of the survey area, the 50 unilateral cases occurred in 24 boys and 26 girls, whereas the 11 bilateral cases occurred in nine girls and only two boys. The reasons for a female preponderance among the bilateral cases remain unclear.

The incidence of retinoblastoma in the United States: 1974 through 1985

We have estimated the incidence of retinoblastoma in the United States from data available form the Surveillance, Epidemiology, and End Results program of the National Cancer Institute, Bethesda, Md (1974 through 1985). The larger number of cases available (220) compared with those of previous US population-based studies enabled us to evaluate change in incidence over time and to more precisely estimate incidence according to various demographic characteristics. The incidence of retinoblastoma has been almost uniform form 1974 to 1985. The average annual incidence of retinoblastoma was 5.8 per million for children younger than 10 years and 10.9 per million for children younger than 5 years. There was no difference in the incidence of retinoblastoma by either sex or race. The overall 5-year cumulative survival rate was 91% (95% confidence interval, 87% to 95%). The data indicate a worsening survival with increasing age at diagnosis, through age 2 years, but a less clear relationship of survival with diagnosis beyond age 2 years.

Retinoblastoma in Great Britain 1969-80: incidence, treatment, and survival

Patients with retinoblastoma diagnosed from 1969 to 1980 have been followed up for periods of up to 17 years. Data from a previous study of patients diagnosed from 1962 to 1968 have been included for analysis of incidence and second primary tumours, and for study of trends in treatment. The registration rate in Britain (which may be about 10% less than the true incidence) is about one in 23,000 live births, approximately 40% of cases being known to be genetic. There is no apparent trend in incidence during the period covered by these two studies. The three-year survival rate in 88%. Patients with bilateral tumours have a better survival rate than those with unilateral tumours for the first few years, but their long-term survival rate is worse because of later deaths from ectopic intracranial retinoblastoma or second primary neoplasms. Older children tend to have a worse prognosis, which is related to the fact that their tumours are diagnosed at a more advanced stage. There is a significantly higher survival rate for boys than for girls; this is partly accounted for by difference in age and stage at diagnosis between the sexes. Children referred to units specialising in the treatment of retinoblastoma have a higher three-year survival rate than those treated at other hospitals. Comparing methods of treatment between the periods 1962-8 and 1969-80, we find there has been a trend towards more conservative treatment. The use of chemotherapy is now usually reserved for recurrences and metastases and for palliative treatment in terminal retinoblastoma.

Second primary tumors in patients with retinoblastoma. A review of the literature

PURPOSE

The aim of this survey was to review the different studies regarding the occurrence of second primary tumours (SPT) among survivors of retinoblastoma.

METHODS

Ovid (Medline, Current contents life, Psychlit, Embase) was searched for the years 1966-1995 using the mesh headings: 'retinoblastoma', 'second primary neoplasms', and 'multiple primary neoplasms'. The inclusion criteria were: the study should involve 50 patients or more and should not be limited to one specific SPT. A checklist with criteria regarding the study design and the results was applied to each study.

RESULTS

Eleven studies were identified which met the inclusion criteria. Thirty-five different types of SPT (Ntotal = 243) were reported. Most of them were osteosarcomas (37.0%), followed by melanomas (7.4%), soft-tissue sarcomas (6.9%), brain tumors (4.5%), fibrosarcomas (3.3%), chondrosarcomas (3.3%), and sarcomas (3.3%). Less frequently reported were leukemias (2:4%), sebaceous cell carcinomas (1.6%), and non-Hodgkin lymphomas (1.6%). Pineoblastoma, which in fact is a trilateral retinoblastoma and not an SPT, was found in 2.4%. Despite the differences, all 11 studies showed a higher incidence of SPT compared to the general population. Only 4 studies were judged to be free from selection bias, reporting a cumulative incidence of SPT of 8.4% 18 years after diagnosis, 15.7% at the age of 20 years, 19% at the age of 35 years, and a relative risk of 15.4 for SPT, respectively.

CONCLUSION

SPT is a serious problem for the survivors of hereditary retinoblastoma and its importance should be recognized in (genetic) counseling of patients.

Incidence and survival of retinoblastoma in The Netherlands: a register based study 1862-1995

AIM

The aim of this study was to determine the (time trends in) incidence and survival of hereditary (familial and sporadic) and non-hereditary retinoblastoma for male and female patients born in the Netherlands between 1862 and 1995.

METHOD

The national retinoblastoma register was updated and now consists of 955 patients. The missing dates of death were obtained from the municipal registers and the Central Bureau of Genealogy in The Hague. Mortality was compared with the Dutch vital statistics.

RESULTS

From 1862 to 1995 no significant differences in incidence for retinoblastoma were found in the hereditary subgroups. Further, no significant differences between males and females were found, both overall and in the hereditary subgroups. The average incidence of retinoblastoma increased until 1944, probably due to incompleteness of the register, and stabilised after 1945 (1 per 17000 live births). From 1900 to 1995 the standardised mortality ratio increased for hereditary retinoblastoma patients from 2.9 to 9.0 and decreased for non-hereditary retinoblastoma patients from 1.9 to 1.0.

CONCLUSION

Although survival for retinoblastoma was significantly better after 1945 than before, in comparison with the Dutch population the mortality between 1900 and 1990 increased for the hereditary and decreased for the non-hereditary retinoblastoma patients.

RB1 gene mutation up-date, a meta-analysis based on 932 reported mutations available in a searchable database

Background

Retinoblastoma, a prototype of hereditary cancer, is the most common intraocular tumour in children and potential cause of blindness from therapeutic eye ablation, second tumours in germ line carrier's survivors, and even death when left untreated. The molecular scanning of RB1 in search of germ line mutations lead to the publication of more than 900 mutations whose knowledge is important for genetic counselling and the characterization of phenotypic-genotypic relationships.

Results

A searchable database (RBGMdb) has been constructed with 932 published RB1 mutations. The spectrum of these mutations has been analyzed with the following results: 1) the retinoblastoma protein is frequently inactivated by deletions and nonsense mutations while missense mutations are the main inactivating event in most genetic diseases. 2) Near 40% of RB1 gene mutations are recurrent and gather in sixteen hot points, including twelve nonsense, two missense and three splicing mutations. The remainder mutations are scattered along RB1, being most frequent in exons 9, 10, 14, 17, 18, 20, and 23. 3) The analysis of RB1 mutations by country of origin of the patients identifies two groups in which the incidence of nonsense and splicing mutations show differences extremely significant, and suggest the involvement of predisposing ethnic backgrounds. 4) A significant association between late age at diagnosis and splicing mutations in bilateral retinoblastoma patients suggests the occurrence of a delayed-onset genotype. 5) Most of the reported mutations in low-penetrance families fall in three groups: a) Mutations in regulatory sequences at the promoter resulting in low expression of a normal Rb; b) Missense and in-frame deletions affecting non-essential sequence motifs which result in a partial inactivation of Rb functions; c) Splicing mutations leading to the reduction of normal mRNA splicing or to alternative splicing involving either true oncogenic or defective (weak) alleles.

Conclusion

The analysis of RB1 gene mutations logged in the RBGMdb has shown relevant phenotype-genotype relationships and provided working hypothesis to ascertain mechanisms linking certain mutations to ethnicity, delayed onset of the disease and low-penetrance. Gene profiling of tumors will help to clarify the genetic background linked to ethnicity and variable expressivity or delayed onset phenotypes.

Risk of cancer among offspring of childhood-cancer survivors. Association of the Nordic Cancer Registries and the Nordic Society of Paediatric Haematology and Oncology

BACKGROUND

Increasing numbers of children with cancer survive and reach reproductive age. However, the risk of cancer (other than retinoblastoma) in the offspring of survivors of childhood and adolescent cancer is uncertain.

METHODS

Using data from national cancer and birth registries, we assessed the risk of cancer among 5847 offspring of 14,652 survivors of cancer in childhood or adolescence diagnosed since the 1940s and 1950s in Denmark, Finland, Iceland, Norway, and Sweden. The offspring were followed up for a diagnosis of cancer for 86,780 person-years, and standardized incidence ratios were calculated.

RESULTS

Among the 5847 offspring, 44 malignant neoplasms were diagnosed (standardized incidence ratio, 2.6; 95 percent confidence interval, 1.9 to 3.5). There were 17 retinoblastomas, yielding a standardized incidence ratio of 37. There were 27 neoplasms other than retinoblastoma (standardized incidence ratio, 1.6; 95 percent confidence interval, 1.1 to 2.4). The second most common primary site of cancer among the offspring was the brain and nervous system, in which eight tumors were observed (standardized incidence ratio, 2.0; 95 percent confidence interval, 0.9 to 3.9.) There were between zero and four apparently sporadic cases of cancer in other primary sites among the offspring. Excluding 4 likely cases of hereditary cancer and 2 subsequent cancers among the offspring with hereditary retinoblastoma, there were 22 sporadic cancers, for a standardized incidence ratio of 1.3 (95 percent confidence interval, 0.8 to 2.0).

CONCLUSIONS

There is no evidence of a significantly increased risk of nonhereditary cancer among the offspring of survivors of cancer in childhood.

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.