Retinoblastoma: A Three-Year-Study at a Brazilian Medical School Hospital

OBJECTIVE:

To present the characteristics and treatment outcomes of patients with retinoblastoma.

METHODS:

A retrospective case series was conducted to review the records of all new patients diagnosed with retinoblastoma between 2003 and 2005. Eyes with early disease, or advanced disease with potential vision were treated with chemotherapy (carboplatin and etoposide) in conjunction with early local therapy (laser or cryo). Radiotherapy was used in cases where the disease did not respond to the above protocols or in recurrent cases. Eyes in the late stage of disease with no potential vision in the initial examination or eyes and where conservative treatment had failed were enucleated.

RESULTS:

In total, we reviewed 28 new cases of retinoblastoma, 15 of which were unilateral and 13 of which were bilateral (46%). These data correspond to a mean of 9.3 new cases per year (0.77 case/month). The mean age at diagnosis was 33.8 months for unilateral cases, and 19.15 months for bilateral cases (p=0.015). Leucocoria was the major presenting symptom (75%). All but one patient with unilateral disease had the affected eye enucleated due to advanced disease (mean follow-up: 39.91 months). Among the 13 bilateral cases, 13 eyes (50%) were enucleated, 11 eyes (42.4%) were saved with chemotherapy in conjunction with local therapy and 2 eyes (7.6%) were saved using external beam radiotherapy (mean follow-up: 41.91 months). In unilateral and bilateral disease, pathology data revealed choroid involvement in 50% and 30%, respectively, and optic nerve invasion in 92% and 50%, respectively.

CONCLUSION:

In this population, retinoblastoma was diagnosed too late and most eyes were consequently enucleated. In cases with bilateral disease, half of the eyes were preserved.     

Familial osteosarcoma associated with 13;14 chromosomal rearrangement

Two prepubertal sisters of American Indian origin developed osteosarcoma at 8 and 12 years of age. This familial occurrence, tumor onset prior to puberty, unusual tumor location in one who also had short stature, and ethnic background all suggest an inborn predisposition to bone cancer rather than a chance occurrence. Rearrangements involving chromosomes #13 and #14 were found in both the surviving proband and mother. Comparison of the arm ratio and prometaphase G-banding patterns of the rearranged chromosomes suggests either deletion of band 14q11.2 or pericentric inversion (with breakpoints at 13q12 and 14q11.2) in the proband's rearranged chromosome, but not in her mother's. Her mother, who had no malignancy, had a typical Robertsonian translocation [t(13;14)(p11;q11)]. Three previously reported children with chromosomal abnormalities developed osteosarcoma at unusually young ages, younger even than in reported sibships with osteosarcoma. The most frequently detected cytogenetic abnormalities in sarcoma tumor cells involve chromosomes #13 and #14. In addition, some cases of bilateral retinoblastoma and familial unilateral retinoblastoma, which are known to be at increased risk for osteosarcoma, are associated with tiny deletions on chromosome #13. Thus, there may be a causal relationship between constitutional loss or rearrangement of genetic material at these breakpoints on chromosomes #13 or #14 and development of osteosarcoma in this family that is similar to that seen in patients with small constitutional chromosomal deletions who develop Wilms' tumor and retinoblastoma.     

Identification of four novel RB1 germline mutations in Korean retinoblastoma patients

To elucidate RB1 germline mutations in Korean retinoblastoma patients, DNA samples from 14 children with bilateral (including three familial cases) and 19 children with unilateral retinoblastoma were analyzed. We found germline mutations in three out of 14 bilateral cases and one out of 19 unilateral cases. There were no germline mutations in the three familial cases. PCR-SSCP from each exon showed bandshifts in four patients which, upon sequencing, were shown to be K616E in exon 19 (c.1846A>G), an AA insertion in exon 7 (c.684-685insAA), R500G in exon 16 (c.1498A>G), and an A insertion in exon 23 (c.2391-2392insA), respectively. Hum Mutat 18:252, 2001.     

Constitutional genomic instability, chromosome aberrations in tumor cells and retinoblastoma

Although retinoblastoma (Rb) is initiated as a result of biallelic inactivation of the RB1 gene, additional genetic events (M3) in tumor cells are indicative of their role in the full transformation of retinal cells. We investigated the constitutional genetic instability by fragile site (FS) expression studies and checked its relationship with loci of tumor cytogenetics in a series of 36 retinoblastoma patients (34 nonfamilial and 2 familial cases). Tumor cytogenetics revealed -13/+13, del/t(13)(q14) (50%), +1/del/t(1p/q) (65%), +6/i(6p) (60%), and del(16)(q13)/(q22 approximately q23) (60%). Conventional cytogenetics in leukocytes revealed constitutional del(13q14) in five unilateral Rb (URB) and one trilateral Rb (TRB). Constitutional del(16)(q22) and t(6;12) were also identified in two cases. Constitutional FS analysis showed a significant increase in the cellular fragility, with high prevalence at 13q14, 3p14, 6p23, 16q22 approximately q23, and 13q22 loci in retinoblastoma patients (P<0.05). Patients with constitutional del(13)(q14) demonstrated higher fragility than those with normal constitution. A strong correlation between loci of constitutional FSs and loci of recurrent chromosomal abnormalities in tumors strengthen and support the proposal that FS loci present as inherent genomic instability in retinoblastoma. The chromosomal changes and resultant genetic mutations, along with RB1 mutation events, probably contribute synergistically to the development and progression of Rb malignancy. Implementation of fluorescence in situ hybridization to nonfamilial Rb on a large scale (113 cases) could detect constitutional RB1 deletion in 12.3% of cases, with equally higher incidence in URB (14.7%) and bilateral Rb (13.6%), demonstrating that the true prevalence of patients with predisposition to RB1 mutation in sporadic URB is definitely higher in our populations. Also, higher incidence of constitutional RB1 deletion mosaicism in unilateral than in bilateral Rb indicates that the constitutional genetic mosaicism in URB should be given serious consideration during genetic counseling.     

Retinoblastoma - a clinical survey and its genetic implications

A clinical, pathological and genetic study was made of 50 patients with retinoblastoma in the Newcastle Hospital region over the period 1931-1970 inclusive. Twenty-seven patients were affected in one eye only; 23 had bilateral tumours. The incidence of the tumour was approximately 1:16,000 live births. Bilateral cases tended to present at a younger age, and were more likely to be familial. In bilateral cases the tumour in the second eye was often detected at an early stage by ophthalmoscopy. In a quarter of the cases there was a considerable interval (up to 10 years) before the second eye was found to be affected. A surprisingly large proportion of eyes with clinically advanced tumour proved to have the tumour histologically confined to the retina. This disparity between clinical and pathological severity emphasises the jusifiability of conservative treatment in the first instance in many cases. Twelve of the 50 patients developed a new tumour, local spread, or reactivation of a treated tumour, over a period ranging from 2 months to 10 years after primary treatment. This finding emphasizes the importance of frequent follow-up of all cases. Follow-up should include the patient's siblings and offspring, even in apparently "sporadic" cases. The of liability to develop retinoblastoma is suggested.     

Identification of 26 new constitutional RB1 gene mutations in Spanish, Colombian, and Cuban retinoblastoma patients

Constitutional mutations in the RB1 gene predispose to retinoblastoma development. Hence genetic screening of retinoblastoma patients and relatives is important for genetic counseling purposes. In addition, RB1 gene mutation studies may help decipher the molecular mechanisms leading to tumors with different degrees of penetrance or expressivity. In the course of genetically screening of 107 hereditary and non-hereditary retinoblastoma patients (11 familiar bilateral, 4 familiar unilateral, 49 sporadic bilateral and 43 sporadic unilateral) and kindred from Spain, Colombia and Cuba, using direct PCR sequencing, we observed 45 distinct mutations and four RB1 deletions in 53 patients (9 familiar bilateral, 2 familiar unilateral, 31 sporadic bilateral and 11 sporadic unilateral). Most of these mutations (26/45, 57%) have not been reported before. In 32 patients, the predisposing mutations correspond to nonsense (mainly CpG transitions) and small insertions or deletions whose expected outcome is a truncated Rb protein that lacks the functional pockets and tail. Five single aminoacid replacements and seventeen mutations affecting splicing sites were also observed in retinoblastoma patients. Two of these sixteen mutations are of unclear pathogenic nature.     

Retinoblastoma and its association with a deletion in chromosome #13: A Survey using high-resolution chromosome techniques

To our knowledge, 20 cases of retinoblastoma associated with a chromosome #13 aberration have been reported. The present study utilized high-resolution prophase banding analysis of 12 additional retinoblastoma patients to determine the occurrence of chromosome aberrations and identify consistently associated clinical abnormalities. Six male and six female patients were studied representing seven cases of bilateral and five cases of unilateral retinoblastoma. One case of unilateral and two cases of bilateral retinoblastoma had detectable cytogenetic abnormalities, all involving an interstitial deletion of 13q14 on the long arm of one chromosome #13. In all five unilateral cases the tumor manifested in the left orbit, and in all seven bilateral cases the left eye was at a more malignantly advanced stage than the right eye. All three cases with a chromosome abnormality had varying degrees of developmental and/or mental retardation, along with at least one other congenital abnormality. In addition to the 12 cases of retinoblastoma, a patient with severe ophthalmologic abnormalities and mild congenital anomalies was studied by the prophase banding technique and found to be partially trisomic for the q13–14 banding regions of chromosome #13. These results further confirm the association of the 13q14 region with gene loci for optic development and indicate that cytogenetic abnormalities may occur even more frequently in retinoblastoma than indicated by the small number of cases reported in the literature.     

Spectrum of gross deletions and insertions in the RB1 gene in patients with retinoblastoma and association with phenotypic expression

Quantitative multiplex PCR and genomic real-time PCR were used to complete an RB1 mutation analysis in 57 of 433 and 72 of 262 patients with hereditary and isolated unilateral retinoblastoma, respectively. These patients were selected because in previous analyses, which focused mainly on the identification of point mutations, no RB1 mutation was found. We identified gross deletions and insertions in peripheral blood DNA from 26 of 57 patients (46%) with hereditary retinoblastoma, and in six of 72 patients (8.3%) with isolated unilateral disease. In addition, we identified 32 somatic mutations in tumor DNA from 31 of 72 patients (43%) with isolated unilateral retinoblastoma. Together with our previous results, we found that gross RB1 alterations were present in the peripheral blood DNA from 65 of 433 (15%) and 17 of 262 (6.5%) patients with bilateral or familial and isolated unilateral retinoblastoma, respectively. Including reported gross deletions, an analysis of the frequency of breakpoints per intron length shows higher densities in introns 13, 16, 23, and 24. Genotype-phenotype analyses showed that on the whole, carriers of gross deletions develop fewer retinoblastomas compared to patients who are heterozygous for other types of RB1 null mutations. Specifically, carriers of cytogenetic and submicroscopic whole gene deletions often have unilateral tumors only. By contrast, almost all patients with gross deletions with one breakpoint in RB1 have bilateral retinoblastoma.     

A microsatellite fluorescent method for linkage analysis in familial retinoblastoma and deletion detection at the RB1 locus in retinoblastoma and osteosarcoma.

Linkage analysis at the retinoblastoma locus (RB1) is essential for identifying individuals at risk and to offer adequate genetic counseling in familial retinoblastoma. It can also be used to detect large deletions involving RB1, which accounts for 15% of the genetic alterations in hereditary retinoblastoma. These studies are usually carried out with lengthy Southern blot analyses of relatively uninformative restriction fragment length polymorphisms. The authors report an alternative, reliable protocol for genotyping the RB1 locus using two pairs of highly informative intragenic and flanking microsatellites linked closely to the RB1 gene, and analysis of the fluorescent-labeled polymerase chain reaction products with automatic sizing technology. This methodology has successfully identified high risk carriers in five of the five pedigrees of familial retinoblastoma studied. In addition, gross deletions affecting the RB1 gene were identified in two of 12 sporadic bilateral retinoblastomas, and loss of heterozygosity at the RB1 locus has been detected in one of three osteosarcomas using the same experimental protocol. The described protocol is simpler and faster than conventional Southern blot methodologies and can identify a larger number of informative cases.     

Comprehensive screening for constitutional RB1 mutations by DHPLC and QMPSF

Constitutional mutations of the RB1 gene are associated with a predisposition to retinoblastoma. It is essential to identify these mutations to provide appropriate genetic counseling in retinoblastoma patients, but this represents an extremely challenging task, as the vast majority of mutations are unique and spread over the entire coding sequence. Since 2001, we have implemented RB1 testing on a routine basis as part of the clinical management of retinoblastoma. As most screening techniques do not meet the requirements for efficient RB1 testing, we have devised a semi-automated denaturing high-performance liquid chromatography (DHPLC) method for point mutation detection combined with a quantitative multiplex PCR of short fluorescent fragments (QMPSF) approach to screen for gene rearrangements. We report the results of this comprehensive screening of all exons and promoter of RB1 in 192 unrelated patients, mostly of French origin. Among 102 bilateral and/or familial cases and 90 unilateral sporadic probands, mutations were identified in 83 (81.5%) and 5 (5.5%) cases, respectively. A total of 43 mutations have not been previously reported. The mutational spectrum was found to be significantly different from previous published series, displaying a surprising amount of splice mutations and large deletions. This study demonstrates the reliability of DHPLC for RB1 analysis, but also illustrates the need for a deletion scanning approach. Finally, considering the benefits to retinoblastoma patients, RB1 testing should be widely implemented in routine healthcare because our study clearly illustrates its feasibility.     

Bilateral retinoblastoma with ectopic intracranial retinoblastoma: Trilateral retinoblastoma

In 11 patients, bilateral retinoblastoma presented at a mean age of 6 months and pineoblastoma at 4 years. We suggest that the hereditary multicentric retinoblastoma arose in vestigeal photoreceptors in the pineal as well as in the hypothetical retinoblasts of the retina. In certain lower animals, the pineal functions as a photoreceptor organ, resembles the retina histologically, and is described as a “third eye”. Hence, the patients we describe may be considered as having “trilateral retinoblastoma”. Two possible variants of this entity were also noted: (1) three children without retinoblastoma who developed pineoblastoma with rosettes and photoreceptor differentiation characteristic of retinoblastoma, and (2) three additional cases involving children who presented with retinoblastoma-like tumors in the suprasellar or parasellar region 2 to 6 months before the discovery of intraocular retinoblastoma. These observations suggest that the retinoblastoma gene confers a previously unappreciated susceptibility to a narrow spectrum of neuroblastic tumors, which usually present in the retina but which can also occur ectopically.     

双环乳晕切口在多中心乳腺良性肿瘤中的应用优势探讨

目的　探讨采用双环乳晕切口在多中心乳腺良性肿瘤临床外科手术中的应用优势。 方法　回顾性分析我院肿瘤外科2016年1月-2017年7月收治的45例行“双环乳晕切口”治疗的“多中心乳腺良性肿瘤”的患者。对所有患者的临床病理因素、手术时间、术中出血量、术后拔管时间、并发症以及术后3个月美容效果、6个月后复发率进行评价。 结果　切除肿瘤数量单侧（5±1）个（2~8个）,双侧（8±2）个（3~13个）。肿瘤长径单侧（5.3±1.3）cm（1.5~8.5 cm）,双侧（3.0±1.5）cm（1.2~6.5 cm）。术中出血量单侧(8.0±2.8)ml（5~15 ml）,双侧(15.4±3.1)ml（10~25 ml）。术后3个月通过门诊和微信随访美容效果,患者满意度在93.3%。术后6个月有37例患者进行彩超复查,其中单侧病变患者22例,复发3例,复发率13.6%;双侧病变患者15例,复发2例,复发率13.3%。 结论　双环乳晕切口在处理分布在不同象限多发性肿瘤、以及有塑形需求的患者人群中具有一定优势。手术安全性高,操作方便,适合临床推广应用。     

A retrospective review of visual outcome and complications in the treatment of retinoblastoma

The aim of this study was to look at the visual outcome and treatment complications of children diagnosed with Retinoblastoma during the years 1985-2003 inclusive. A retrospective review of all patients records was performed. Patient characteristics, treatment methods and complications were recorded. Twenty eight children presented to Temple street Hospital between 1985-2003. Six of these infants had bilateral tumours. The mean age at presentation was 23.7 months. Sixty-nine percent presented with Leucocoria, of these 33% also had a squint. The mean duration of symptoms was only known in 58% and this figure was approximately 19.8 months. Enucleation was performed in 24 eyes of 24 patients. Three patients required adjuvant chemotherapy post enucleation. Two eyes was treated with external beam radiation and one eye with plaque radiotherapy. One eye (second eye) was treated with systemic chemotherapy and radiation. Five eyes of three patients were treated with systemic chemotherapy followed by adjuvant Argon laser, cryotherapy and diode laser to each eye.The complications of each treatment group was recorded. The visual outcome in the salvaged eyes was favourable. There were no deaths recorded. Though chemotherapy with adjuvant local treatments provide adequate treatment for early tumours, enucleation still plays a major role in the treatment of Retinoblastoma. The total eye salvage rate in this study was 29% with an enucleation rate of 90% in unilateral cases and 33% in bilateral cases. Sixty-six percent of bilateral eyes affected were salvaged. Seventy-one percent of tumours were diagnosed after a parent noticed a gross abnormality of the eye. This highlights the possible need for screening for retinoblastoma in the infant population.     

Patient understanding of genetic information influences reproductive decision making in retinoblastoma

Background: Retinoblastoma is the most common malignant tumour of the eye in childhood, with nearly all bilateral tumours and around 17% to 18% of unilateral tumours due to an oncogenic mutation in the RB1 gene in the germline. Genetic testing enables accurate risk assessment and optimal clinical management for the affected individual, siblings, and future offspring. Material and Methods: We carried out the first UK‐wide audit of understanding of genetic testing in individuals with retinoblastoma. A total of 292 individuals aged 16 to 45 years were included. Results: Patients with bilateral disease were significantly more likely to understand the implications of retinoblastoma for siblings and children. There was a significant association between not knowing the results of genetic testing or not understanding the implications and not having children, particularly in women. Surprisingly, this was also true for individuals treated for unilateral disease with a low risk of retinoblastoma for their offspring. Conclusion: We are concerned that individuals may be making life choices based on insufficient information regarding risks of retinoblastoma and reproductive options. We suggest that improvement in transition care is needed to enable individuals to make informed reproductive decisions and to ensure optimal care for children born at risk of retinoblastoma.     

Excess of cancer deaths in grandparents of patients with retinoblastoma.

An excess of cancer deaths was found in grandparents of 308 children with retinoblastoma. This excess was found in all types of retinoblastoma, unilateral and bilateral, sporadic and familial. We postulated that the excess could be the result of a factor of susceptibility to cancer, different from the retinoblastoma gene, which would increase the mutation rate in retinal and germ cells as well as in other tissues.     

Mutational mosaicism and genetic counseling in retinoblastoma.

Mutations may arise throughout an organism's life cycle. Typically, sporadic meiotic mutations give rise to individuals with all their germinal and somatic cells bearing the mutant gene. These mutations may be amorphs (with full penetrance and expressivity) or hypomorphs (with reduced penetrance and expressivity). Mutational mosaicism, however, involves the origin of mutations occurring during mitosis, whether in the parent at some stage prior to reproductive maturity or in the offspring at some time following fertilization. The phenotypic expression and transmission of these new mutations are dependent on the proportion of cells bearing the mutant gene as well as the location of these cells in somatic and/or germinal tissues. Mutational mosaicism was used as a developmental model to analyze 1,500 sporadic and 179 familial cases of retinoblastoma from the world literature. This model provided an interpretation for the origin, onset, and transmissibility of the sporadic unilateral retinoblastoma cases, which represent over 60% of all retinoblastoma patients. The model also permits a reclassification of all transmissible types of retinoblastoma; based on this classification, more accurate risk figures for genetic counseling can be offered. In addition, mutational mosaicism can be extended as a model to other autosomal dominant and X-linked mutations.     

Clinical experiences of pheochromocytoma in Korea

Purpose

We report herein 119 patients with pheochromocytoma at our institute over the last 23 years.

Materials and Methods

Between 1986 and 2009, 119 patients were diagnosed with pheochromocytoma at our institute. We reviewed the medical records of these patients.

Results

Of 119 patients, 45 were male and 74 were female, and mean age was 43.83 ± 13.49 years. Forty-three patients (36.1%) were diagnosed incidentally, and 8 patients (6.7%) were found to have familial pheochromocytoma. The mean dimension of the tumors was 5.89 ± 3.18 cm. 4 patients had bilateral tumors; three of these patients were found to have familial pheochromocytoma and 1 patient was diagnosed with malignant pheochromocytoma. A total of eight patients (6.7%) were found to have malignant pheochromocytoma. In 1 patient, metastasis to a lymph node was found at the time of diagnosis. Metastases were found at a mean of 49 ± 25.83 (6-75) months after surgery in the other seven patients. 6 patients died of malignant pheochromocytoma at a mean of 31 ± 28.71 months (1-81) after diagnosis, and the other 2 patients survived for 15 and 24 months, respectively.

Conclusion

Approximately 35% of patients with pheochromocytoma are diagnosed incidentally, and the number of detected cases is increasing. Although familial pheochromocytoma was found only in 6.7% of the patients, genetic testing should be considered in all patients, especially in patients with a family history, young age, or multifocal, bilateral, extra-adrenal, or malignant tumors. Given that malignant pheochromocytomas are frequently diagnosed during the follow-up period, long-term follow-up is necessary to confirm the absence of recurrence or metastasis.     

Enhanced Sensitivity for Detection of Low‐Level Germline Mosaic RB1 Mutations in Sporadic Retinoblastoma Cases Using Deep Semiconductor Sequencing

Sporadic retinoblastoma (RB) is caused by de novo mutations in the RB1 gene. Often, these mutations are present as mosaic mutations that cannot be detected by Sanger sequencing. Next‐generation deep sequencing allows unambiguous detection of the mosaic mutations in lymphocyte DNA. Deep sequencing of the RB1 gene on lymphocyte DNA from 20 bilateral and 70 unilateral RB cases was performed, where Sanger sequencing excluded the presence of mutations. The individual exons of the RB1 gene from each sample were amplified, pooled, ligated to barcoded adapters, and sequenced using semiconductor sequencing on an Ion Torrent Personal Genome Machine. Six low‐level mosaic mutations were identified in bilateral RB and four in unilateral RB cases. The incidence of low‐level mosaic mutation was estimated to be 30% and 6%, respectively, in sporadic bilateral and unilateral RB cases, previously classified as mutation negative. The frequency of point mutations detectable in lymphocyte DNA increased from 96% to 97% for bilateral RB and from 13% to 18% for unilateral RB. The use of deep sequencing technology increased the sensitivity of the detection of low‐level germline mosaic mutations in the RB1 gene. This finding has significant implications for improved clinical diagnosis, genetic counseling, surveillance, and management of RB.     

pRB detection as a common event in human retinoblastomas: an immunohistochemical study

Approximately 30% of the cases of retinoblastoma (RB), the childhood eye cancer, are inherited and are manifested by unilateral or bilateral tumor. In sporadic tumors, accounting for 70% of cases, only one eye is affected. RB has three histological features: undifferentiated anaplastic cells, retinoblast pattern, and differentiated pattern characterized by Flexner Wintersteiner rosettes (FWR). Currently, results concerning phosphoprotein RB (pRB) expression in RB tumors are contradictory. In this study we detected pRB immunohistochemically in 10 tumors from bilateral or unilateral RBs, which did not show gross chromosomal alterations in cytogenetic studies. Interestingly, pRB was undetectable in only one tumor where we found distinct histological features. Our results suggest that pRB immunopositivity may be common in these tumors. However, it does not rule out the possibility that pRB is functionally inactive in some cases. This may be due to the protein being present in phosphorylated form or being altered by point mutations not affecting its expression. Another possibility is that mechanisms other than RB1 gene changes may lead to retinoblastoma because not all cases of retinoblastoma show gene alterations. Together these findings may be useful in understanding the molecular mechanisms associated with this type of pediatric tumor.     

Mutational mosaicism and genetic counseling in retinoblastoma

Mutations may arise throughout an organism's life cycle. Typically, sporadic meiotic mutations give rise to individuals with all their germinal and somatic cells bearing the mutant gene. These mutations may be amorphs (with full penetrance and expressivity) or hypomorphs (with reduced penetrance and expressivity). Mutational mosaicism, however, involves the origin of mutations occurring during mitosis, whether in the parent at some stage prior to reproductive maturity or in the offspring at some time following fertilization. The phenotypic expression and transmission of these new mutations are dependent on the proportion of cells bearing the mutant gene as well as the location of these cells in somatic and/or germinal tissues. Mutational mosaicism was used as a developmental model to analyze 1,500 sporadic and 179 familial cases of retinoblastoma from the world literature. This model provided an interpretation for the origin, onset, and transmissibility of the sporadic unilateral retinoblastoma cases, which represent over 60% of all retinoblastoma patients. The model also permits a reclassification of all transmissible types of retinoblastoma; based on this classification, more accurate risk figures for genetic counseling can be offered. In addition, mutational mosaicism can be extended as a model to other autosomal dominant and X-linked mutations.