Genetic Diagnosis of Retinoblastoma Using Aqueous Humour-Findings from an Extended Cohort.

The identification of somatic RB1 variation is crucial to confirm the heritability of retinoblastoma. We and others have previously shown that, when tumour DNA is unavailable, cell-free DNA (cfDNA) derived from aqueous humour (AH) can be used to identify somatic RB1 pathogenic variation. Here we report RB1 pathogenic variant detection, as well as cfDNA concentration in an extended cohort of 75 AH samples from 68 patients. We show cfDNA concentration is highly variable and significantly correlated with the collection point of the AH. Cell-free DNA concentrations above 5 pg/µL enabled the detection of 93% of known or expected RB1 pathogenic variants. In AH samples collected during intravitreal chemotherapy treatment (Tx), the yield of cfDNA above 5 pg/µL and subsequent variant detection was low (≤46%). However, AH collected by an anterior chamber tap after one to three cycles of primary chemotherapy (Dx1+) enabled the detection of 75% of expected pathogenic variants. Further limiting our analysis to Dx1+ samples taken after ≤2 cycles (Dx ≤ 2) provided measurable levels of cfDNA in all cases, and a subsequent variant detection rate of 95%. Early AH sampling is therefore likely to be important in maximising cfDNA concentration and the subsequent detection of somatic RB1 pathogenic variants in retinoblastoma patients undergoing conservative treatment.

Differences in Childhood Growth Parameters Between Patients With Somatic and Heritable Retinoblastoma.

Purpose: Little is known regarding differences in childhood growth between somatic and heritable retinoblastoma (Rb) populations. We aimed to compare childhood growth parameters between somatic and heritable Rb cohorts at birth and at time of diagnosis with Rb. Methods: A multinational, longitudinal cohort study was conducted with patients from 11 centers in 10 countries who presented with treatment naïve Rb from January to December 2019. Variables of interest included age, sex, and size characteristics at birth and at time of presentation, as well as germline mutation status. After Bonferroni correction, results were statistically significant if the P value was less than 0.005. Results: We enrolled 696 patients, with 253 analyzed after exclusion criteria applied. Between somatic (n = 39) and heritable (n = 214) Rb cohorts, with males and females analyzed separately, there was no significant difference in birth weight percentile, weight percentile at time of diagnosis, length percentile at time of diagnosis, weight-for-length percentile at time of diagnosis, or change of weight percentile from birth to time of diagnosis. Patients with heritable Rb had a smaller mean weight percentile at birth and smaller mean weight and length percentiles at time of diagnosis with Rb, although this difference was not statistically significant. All cohorts experienced a slight negative change of weight percentile from birth to time of diagnosis. No cohort mean percentiles met criteria for failure to thrive, defined as less than the 5th percentile. Conclusions: Children with Rb seem to have normal birth and childhood growth patterns. There is no definitive evidence that somatic or heritable Rb has a biological or environmental impact on childhood growth parameters.

An overview of RB1 transcript alterations detected during retinoblastoma genetic screening.

Identification of pathogenic RB1 variants aids in the clinical management of families with retinoblastoma. We routinely screen DNA for RB1 variants, but transcript analysis can also be used for variant screening, and to help decide variant pathogenicity. DNA was screened by conformation analysis followed by Sanger sequencing. Large deletion/insertions were detected by polymorphism analysis, MLPA and quantitative-PCR. Methylation-specific PCR was used to detect hypermethylation. RNA screening was performed when a DNA pathogenic variant was missing, or to determine effects on splicing.Two hundred and thirteen small coding variants were predicted to affect splicing in 207 patients. Splice donor (sd) variants were nearly twice as frequent as splice acceptor (sa) with the most affected positions being sd + 1 and sa-1. Some missense and nonsense codons altered splicing, while some splice consensus variants did not. Large deletion/insertions can disrupt splicing, but RNA analysis showed that some of these are more complex than indicated by DNA testing. RNA screening found pathogenic variants in 53.8% of samples where DNA analysis did not. RB1 splicing is altered by changes at consensus splice sites, some missense and nonsense codons, deep intronic changes and large deletion/insertions. Common alternatively spliced transcripts may complicate analysis. An effective molecular screening strategy would include RNA analysis to help determine pathogenicity.

Changing trends in pseudoretinoblastoma diagnoses: A 10 year review from the United Kingdom.

AIM: To study the different types and frequency of pseudoretinoblastoma (pseudoRB) lesions who present to a retinoblastoma centre due to concern that the condition may be retinoblastoma. METHODS: A retrospective chart review of 341 patients presenting sporadically to the Royal London Hospital from January 2009 to December 2018. RESULTS: 220 patients (65%) were confirmed to have retinoblastoma, while 121 (35%) had pseudoRB. There were 23 differential diagnoses in total. The top 3 differential diagnoses were Coats' disease (34%), Persistent Foetal Vasculature (PFV) (17%) and Combined Hamartoma of Retina and Retinal Pigment Epithelium (CHR-RPE) (13%). PseudoRBs differed with age at presentation. Under the age of 1 (n = 42), the most likely pseudoRB conditions were PFV (36%), Coats' disease (17%) and CHR-RPE (12%). These conditions were also the most common simulating conditions between the ages of 1 and 2 (n = 21), but Coats' disease was the most common in this age group (52%), followed by CHR-RPE (19%) and PFV (14%). Between the ages of 2 and 5 (n = 32), Coats' disease remained the most common (44%) pseudoRB lesion followed by CHR-RPE (13%), or PFV, Retinal Astrocytic Hamartoma (RAH), familial exudative vitreoretinopathy (FEVR) (all 6.3%). Over the age of 5 (n = 26), pseudoRBs were most likely to be Coats' disease (35%), RAH (12%), Uveitis, CHR-RPE, FEVR (all 7.7%). CONCLUSION: 35% of suspected retinoblastoma cases are pseudoRB conditions. Overall, Coats' disease is the most common pseudoRB condition, followed by PFV. Hamartomas (CHR-RPE & RAH) are more prevalent in this cohort, reflecting improvements in diagnostic accuracy from referring ophthalmologists.

Systemic adjuvant chemotherapy for advanced malignant ocular medulloepithelioma.

BACKGROUND: Ocular medulloepithelioma (diktyoma) is a rare and potentially malignant paediatric tumour of the non-pigmented ciliary epithelium. Adjuvant chemotherapy can be given in advanced cases, but the indications and regimens remain to be defined. The aim was to identify whether adjuvant chemotherapy offers treatment benefit in advanced ocular medulloepithelioma. METHODS: This was a retrospective case series of subjects referred to a single specialist ocular oncology centre for advanced ocular medulloepithelioma subsequently treated with enucleation, including those needing adjuvant systemic vincristine, etoposide and carboplatin. A case-note review was performed for included subjects meeting referral criteria. The outcomes were histopathology characteristics, recurrence, metastases and survival. RESULTS: Between March 2010 and June 2017, four male patients (mean age 31 months) underwent enucleation for ocular medulloepithelioma. Adjuvant chemotherapy was commenced in 3 patients (75%) due to malignant histopathological features. With a mean follow-up time of 81.5 months (median 71 months, range 49-135 months) none of the patients have had recurrence, metastases or death from the tumour. CONCLUSIONS: This series is unique in reporting the management of advanced malignant ocular medulloepithelioma with adjuvant systemic vincristine, etoposide and carboplatin for advanced tumours with malignant features. This regimen appears to be safe and may be effective in preventing metastatic spread.

Retinoblastoma and vision.

The assessment of vision has a growing importance in the management of retinoblastoma in the era of globe-conserving therapy, both prior to and after treatment. As survival rates approach 98-99% and globe salvage rates reach ever-higher levels, it is important to provide families with information regarding the visual outcomes of different treatments. We present an overview of the role of vision in determining the treatment given and the impact of complications of treatment. We also discuss screening and treatment strategies that can be used to maximise vision.

The role of maternal age & birth order on the development of unilateral and bilateral retinoblastoma: a multicentre study.

BACKGROUND/OBJECTIVES: Retinoblastoma is a common childhood intraocular malignancy, the bilateral form of which most commonly results from a de novo germline pathogenic variant in the RB1 gene. Both advanced maternal age and decreasing birth order are known to increase the risk of de novo germline pathogenic variants, while the influence of national wealth is understudied. This cohort study aimed to retrospectively observe whether these factors influence the ratio of bilateral retinoblastoma cases compared to unilateral retinoblastoma, thereby inferring an influence on the development of de novo germline pathogenic variants in RB1. SUBJECTS/METHODS: Data from 688 patients from 11 centres in 10 countries were analysed using a series of statistical methods. RESULTS: No associations were found between advanced maternal age, birth order or GDP per capita and the ratio of bilateral to unilateral retinoblastoma cases (p values = 0.534, 0.201, 0.067, respectively), indicating that these factors do not contribute to the development of a de novo pathogenic variant. CONCLUSIONS: Despite a lack of a definitive control group and genetic testing, this study demonstrates that advanced maternal age, birth order or GDP per capita do not influence the risk of developing a bilateral retinoblastoma.

Ruthenium plaque radiotherapy in the current era of retinoblastoma treatment.

BACKGROUND: Two major treatment modalities for retinoblastoma, intraarterial chemotherapy (IAC) and intravitreal chemotherapy (IVitC), have superseded external beam radiotherapy for eye salvage. In this new setting our objectives were to evaluate the indications for plaque radiotherapy, complications, and recurrence rates. METHODS: Retrospective detailed review of patient's charts was performed for all subjects treated with plaque radiotherapy for retinoblastoma between January 2015 and December 2020. RESULTS: A total of 12 eyes of 12 patients were included. Mean age at plaque insertion was 45 months (median 29, range 17-150). The treatment dose was 40 Gy to the tumor apex. The indication for plaque radiotherapy was salvage therapy in 11 eyes (92%) and primary treatment in one eye (8%). At last follow-up from plaque insertion (mean 36 months, range 3-67), four (33%) patients had visual acuity better than 0.5 LogMAR and four (33%) had visual acuity worse than 1.0 LogMAR. Radiation-related complications were: one (8%) vitreous haemorrhage, two (16%) non-proliferative radiation retinopathy and one (8%) cataract. Recurrence was detected in four (33%) patients at a mean of 7.8 months (median 5, range 1-20) post-plaque. Globe salvage rate was 75%, as three eyes required enucleation, one to treat recurrence of the tumor treated with plaque and two to treat recurrence of other tumors. CONCLUSIONS: In the current era of retinoblastoma management, a role for plaque radiotherapy remains for salvage or primary treatment in eyes with localised active tumor, providing tumor control in 66%. Close observation is recommended to both detect recurrence and radiation-related complications.

PRELP Regulates Cell-Cell Adhesion and EMT and Inhibits Retinoblastoma Progression.

Retinoblastoma (RB) is the most common intraocular pediatric cancer. Nearly all cases of RB are associated with mutations compromising the function of the RB1 tumor suppressor gene. We previously demonstrated that PRELP is widely downregulated in various cancers and our in vivo and in vitro analysis revealed PRELP as a novel tumor suppressor and regulator of EMT. In addition, PRELP is located at chromosome 1q31.1, around a region hypothesized to be associated with the initiation of malignancy in RB. Therefore, in this study, we investigated the role of PRELP in RB through in vitro analysis and next-generation sequencing. Immunostaining revealed that PRELP is expressed in Müller glial cells in the retina. mRNA expression profiling of PRELP-/- mouse retina and PRELP-treated RB cells found that PRELP contributes to RB progression via regulation of the cancer microenvironment, in which loss of PRELP reduces cell-cell adhesion and facilitates EMT. Our observations suggest that PRELP may have potential as a new strategy for RB treatment.

Sex, gender, and retinoblastoma: analysis of 4351 patients from 153 countries.

OBJECTIVE: To investigate in a large global sample of patients with retinoblastoma whether sex predilection exists for this childhood eye cancer. METHODS: A cross-sectional analysis including 4351 treatment-naive retinoblastoma patients from 153 countries who presented to 278 treatment centers across the world in 2017. The sex ratio (male/female) in the sample was compared to the sex ratio at birth by means of a two-sided proportions test at global level, country economic grouping, continent, and for selected countries. RESULTS: For the entire sample, the mean retinoblastoma sex ratio, 1.20, was higher than the weighted global sex ratio at birth, 1.07 (p < 0.001). Analysis at economic grouping, continent, and country-level demonstrated differences in the sex ratio in the sample compared to the ratio at birth in lower-middle-income countries (n = 1940), 1.23 vs. 1.07 (p = 0.019); Asia (n = 2276), 1.28 vs. 1.06 (p < 0.001); and India (n = 558), 1.52 vs. 1.11 (p = 0.008). Sensitivity analysis, excluding data from India, showed that differences remained significant for the remaining sample (χ2 = 6.925, corrected p = 0.025) and for Asia (χ2 = 5.084, corrected p = 0.036). Excluding data from Asia, differences for the remaining sample were nonsignificant (χ2 = 2.205, p = 0.14). CONCLUSIONS: No proof of sex predilection in retinoblastoma was found in the present study, which is estimated to include over half of new retinoblastoma patients worldwide in 2017. A high male to female ratio in Asian countries, India in specific, which may have had an impact on global-level analysis, is likely due to gender discrimination in access to care in these countries, rather than a biological difference between sexes.

Defining High-risk Retinoblastoma: A Multicenter Global Survey.

IMPORTANCE: High-risk histopathologic features of retinoblastoma are useful to assess the risk of systemic metastasis. In this era of globe salvage treatments for retinoblastoma, the definition of high-risk retinoblastoma is evolving. OBJECTIVE: To evaluate variations in the definition of high-risk histopathologic features for metastasis of retinoblastoma in different ocular oncology practices around the world. DESIGN, SETTING, AND PARTICIPANTS: An electronic web-based, nonvalidated 10-question survey was sent in December 2020 to 52 oncologists and pathologists treating retinoblastoma at referral retinoblastoma centers. INTERVENTION: Anonymized survey about the definition of high-risk histopathologic features for metastasis of retinoblastoma. MAIN OUTCOMES AND MEASURES: High-risk histopathologic features that determine further treatment with adjuvant systemic chemotherapy to prevent metastasis. RESULTS: Among the 52 survey recipients, the results are based on the responses from 27 individuals (52%) from 24 different retinoblastoma practices across 16 countries in 6 continents. The following were considered to be high-risk features: postlaminar optic nerve infiltration (27 [100%]), involvement of optic nerve transection (27 [100%]), extrascleral tissue infiltration (27 [100%]), massive (≥3 mm) choroidal invasion (25 [93%]), microscopic scleral infiltration (23 [85%]), ciliary body infiltration (20 [74%]), trabecular meshwork invasion (18 [67%]), iris infiltration (17 [63%]), anterior chamber seeds (14 [52%]), laminar optic nerve infiltration (13 [48%]), combination of prelaminar and laminar optic nerve infiltration and minor choroidal invasion (11 [41%]), minor (<3 mm) choroidal invasion (5 [19%]), and prelaminar optic nerve infiltration (2 [7%]). The other histopathologic features considered high risk included Schlemm canal invasion (4 [15%]) and severe anaplasia (1 [4%]). Four respondents (15%) said that the presence of more than 1 high-risk feature, especially a combination of massive peripapillary choroidal invasion and postlaminar optic nerve infiltration, should be considered very high risk for metastasis. CONCLUSIONS AND RELEVANCE: Responses to this nonvalidated survey conducted in 2020-2021 showed little uniformity in the definition of high-risk retinoblastoma. Postlaminar optic nerve infiltration, involvement of optic nerve transection, and extrascleral tumor extension were the only features uniformly considered as high risk for metastasis across all oncology practices. These findings suggest that the relevance about their value in the current scenario with advanced disease being treated conservatively needs further evaluation; there is also a need to arrive at consensus definitions and conduct prospective multicenter studies to understand their relevance.

The Effects of Breastfeeding on Retinoblastoma Development: Results from an International Multicenter Retinoblastoma Survey.

The protective effects of breastfeeding on various childhood malignancies have been established but an association has not yet been determined for retinoblastoma (RB). We aimed to further investigate the role of breastfeeding in the severity of nonhereditary RB development, assessing relationship to (1) age at diagnosis, (2) ocular prognosis, measured by International Intraocular RB Classification (IIRC) or Intraocular Classification of RB (ICRB) group and success of eye salvage, and (3) extraocular involvement. Analyses were performed on a global dataset subgroup of 344 RB patients whose legal guardian(s) consented to answer a neonatal questionnaire. Patients with undetermined or mixed feeding history, family history of RB, or sporadic bilateral RB were excluded. There was no statistically significant difference between breastfed and formula-fed groups in (1) age at diagnosis (p = 0.20), (2) ocular prognosis measures of IIRC/ICRB group (p = 0.62) and success of eye salvage (p = 0.16), or (3) extraocular involvement shown by International Retinoblastoma Staging System (IRSS) at presentation (p = 0.74), lymph node involvement (p = 0.20), and distant metastases (p = 0.37). This study suggests that breastfeeding neither impacts the sporadic development nor is associated with a decrease in the severity of nonhereditary RB as measured by age at diagnosis, stage of disease, ocular prognosis, and extraocular spread. A further exploration into the impact of diet on children who develop RB is warranted.

Strabismus as a Presenting Sign in Retinoblastoma.

PURPOSE: To report the presenting signs of retinoblastoma in a large cohort of patients who underwent orthoptic assessment at presentation. METHODS: A retrospective medical chart review was conducted on 131 patients with retinoblastoma who presented consecutively to a single institution during a 6-year period. The main outcome measure was the presenting sign(s) of the disease. RESULTS: Of 131 patients with retinoblastoma, 88 presented with unilateral disease and 43 presented with bilateral disease (mean ages: 22.7 and 14.8 months, respectively). Leukocoria was the presenting sign in 56% of patients, leukocoria and strabismus in 18%, strabismus in 13%, inflammation in 8%, and "other" signs in 5%. The fovea was affected by the retinoblastoma tumor or its sequelae in 75% of patients. Patients who presented with strabismus were significantly more likely to have foveal involvement than patients who presented with leukocoria alone (P = .001). Thirty-one percent of patients had strabismus as a component of their presentation; 63% had exotropia, 23% had esotropia, and 14% had variable strabismus. The percentage of patients with strabismus increased to 66% when small angle and variable strabismus were also considered. Patients with inflammation had worse ocular survival (P < .05). CONCLUSIONS: This study assessed the combination of leukocoria and strabismus as presenting features of retinoblastoma. Foveal involvement is common in patients who have strabismus and may influence decision-making regarding globe salvage. The authors confirmed that exotropia is more common than esotropia in retinoblastoma in the largest cohort to have undergone an orthoptic assessment. [J Pediatr Ophthalmol Strabismus. 2021;58(5):324-330.].

The frequency of severe corneal opacities in premature infants.

PURPOSE: To study the frequency and possible causes of severe corneal opacities in premature infants undergoing retinopathy of prematurity (ROP) screening in the neonatal intensive care unit (NICU) at a single institution. METHODS: The medical records of all infants screened for ROP in the NICU between January 2015 and March 2019 were reviewed retrospectively. Criteria for screening were gestational age (GA) of <32 weeks or birth weight (BW) <1501 g. Characteristics of premature infants with severe corneal opacities were extracted from the record. RESULTS: A total of 445 premature infants were screened during the 51-month period. The prevalence of severe corneal opacities was 1.4% (6 infants). The median GA of the affected infants was 24.5 weeks (range, 23-32), and the mean BW was 624 g (range, 500-860 g). Two infants had lagophthalmos; their corneal opacity was unilateral. All the infants were under continuous positive airway pressure (CPAP) for a prolonged period. All 4 infants with bilateral corneal opacities required treatment for severe ROP-laser (n =1), bevacizumab injection (n = 1), or both (n = 2). CONCLUSIONS: Severe corneal opacities in premature infants are rare but potentially sight threatening, because they can hinder the retinal examination. Lagophthalmos-related exposure keratopathy is an obvious risk factor. CPAP therapy may be another risk factor leading to the development of severe corneal opacities. Identification of infants at risk and prompt commencement of lubricants is necessary to avoid long-term corneal opacities.

MYCN amplification levels in primary retinoblastoma tumors analyzed by Multiple Ligation-dependent Probe Amplification.

Background: Retinoblastoma (Rb) is a childhood tumor of the developing retina where predisposition is caused by RB1 pathogenic variants. MYCN amplification (MYCNA) has been implicated in around 2% of sporadic unilateral Rb tumors with no detectable RB1 variants. We audited data from tumors collected between 1993 and 2019 to determine if this is the case for patients treated at Barts Health NHS Trust, and how often it occurred alongside RB1 variants. Materials and methods: Screening for MYCNA was carried out by Multiple Ligation Probe Analysis of tumor and blood samples collected for RB1 genetic screening. The cohort consisted of 149 tumors, of which 114 had matched blood samples. Results: 10/149 (6.7%) tumors were positive for MYCNA in a population containing a disproportionate number of cases negative for RB1 pathogenic variants. Of 65 unbiased tumors collected from 2014 to 2019, 2 (3.1%) had MYCNA. All MYCNA samples were from sporadic, unilateral patients and 3/10 (30%) had RB1 pathogenic variants. MYCNA was not detected in any blood sample. No MYCNA tumor had 6p gain which is usually a common alteration in Rbs. Conclusions:MYCNA occurs in a small fraction of Rbs and can occur in the presence of pathogenic RB1 variants. However, where it occurs alongside RB1 alterations, the age of onset appears to be later. MYCNA has yet to be seen as a heritable change. In sporadic cases with early diagnosis, Rbs with no RB1 pathogenic variant identified should be tested for MYCNA. Conversely, tumors with MYCNA should still be screened for RB1 pathogenic variants.

Lag Time between Onset of First Symptom and Treatment of Retinoblastoma: An International Collaborative Study of 692 Patients from 10 Countries.

BACKGROUND: The relationship between lag time and outcomes in retinoblastoma (RB) is unclear. In this study, we aimed to study the effect of lag time between onset of symptoms and diagnosis of retinoblastoma (RB) in countries based on their national-income and analyse its effect on the outcomes. METHODS: We performed a prospective study of 692 patients from 11 RB centres in 10 countries from 1 January 2019 to 31 December 2019. RESULTS: The following factors were significantly different among different countries based on national-income level: age at diagnosis of RB (p = 0.001), distance from home to nearest primary healthcare centre (p = 0.03) and mean lag time between detection of first symptom to visit to RB treatment centre (p = 0.0007). After adjusting for country income, increased lag time between onset of symptoms and diagnosis of RB was associated with higher chances of an advanced tumour at presentation (p < 0.001), higher chances of high-risk histopathology features (p = 0.003), regional lymph node metastasis (p < 0.001), systemic metastasis (p < 0.001) and death (p < 0.001). CONCLUSIONS: There is a significant difference in the lag time between onset of signs and symptoms and referral to an RB treatment centre among countries based on national income resulting in significant differences in the presenting features and clinical outcomes.

Whole-Genome Sequencing of Retinoblastoma Reveals the Diversity of Rearrangements Disrupting RB1 and Uncovers a Treatment-Related Mutational Signature.

The development of retinoblastoma is thought to require pathological genetic changes in both alleles of the RB1 gene. However, cases exist where RB1 mutations are undetectable, suggesting alternative pathways to malignancy. We used whole-genome sequencing (WGS) and transcriptomics to investigate the landscape of sporadic retinoblastomas derived from twenty patients, sought RB1 and other driver mutations and investigated mutational signatures. At least one RB1 mutation was identified in all retinoblastomas, including new mutations in addition to those previously identified by clinical screening. Ten tumours carried structural rearrangements involving RB1 ranging from relatively simple to extremely complex rearrangement patterns, including a chromothripsis-like pattern in one tumour. Bilateral tumours obtained from one patient harboured conserved germline but divergent somatic RB1 mutations, indicating independent evolution. Mutational signature analysis showed predominance of signatures associated with cell division, an absence of ultraviolet-related DNA damage and a profound platinum-related mutational signature in a chemotherapy-exposed tumour. Most RB1 mutations are identifiable by clinical screening. However, the increased resolution and ability to detect otherwise elusive rearrangements by WGS have important repercussions on clinical management and advice on recurrence risks.

Prognostic Information for Known Genetic Carriers of RB1 Pathogenic Variants (Germline and Mosaic).

PURPOSE: To compare the number of tumors per eye for mosaic carriers of RB1 pathogenic variants with full germline variants and the conversion from unilateral to bilateral disease. DESIGN: Retrospective cohort study comparing patients with retinoblastoma and different genetic subtypes: high penetrance (HP), low penetrance (LP), and mosaicism. PARTICIPANTS: Data were analyzed between 1992 and 2018 at the Retinoblastoma Unit, Royal London Hospital, London, United Kingdom. All familial patients had a parent with a known pathogenic variant even if the parent did not manifest the disease. MAIN OUTCOME MEASURES: Number of tumors per eye in children who developed retinoblastoma in that eye. Other outcomes included total number of tumors per patient, age at diagnosis, laterality at presentation and later, sex, and stage according to International Intraocular Retinoblastoma Classification. RESULTS: A total of 111 patients were included: 64 full germline, familial patients (53 HP and 11 LP) and 47 mosaic patients. Twelve HP patients (23%) were unilateral, and 8 of 12 patients (67%) developed tumors in their previously unaffected eye. A total of 34 mosaic patients (72%) were unilateral, and only 2 (6%) developed tumors in their unaffected eye. Age at diagnosis was higher in mosaic patients (median, 22 months) than in HP patients (median 7) (P < 0.00002). The number of tumors per eye was fewer in patients with mosaic alleles (median, 1.0; range, 1-6) compared with patients with HP alleles (median, 3.0; range, 1-8) (P < 0.0003). All 3 children (4 eyes) with mosaicism and more than 2 tumors per eye had high levels of mosaicism. CONCLUSIONS: Children with mosaic alleles have fewer tumors per eye compared with those with known high-penetrant pathogenic variants and are more likely to remain unilateral. The level of mosaicism has an impact on laterality and number of tumors.