Unusual anterior and posterior segment features of coats disease.

PURPOSE: To report the clinical course and management of unusual anterior and posterior segment features of Coats disease and their relation to the age of the patients to increase the awareness towards these rare clinical features rarely described in the current literature. METHODS: A retrospective descriptive review of 45 eyes of 45 patients affected by Coats disease was conducted at the Retinoblastoma Referral Center and Ophthalmology Unit of the University of Siena in Italy analyzing data from 2000 to 2022. Medical records and images were revised to find some cases presenting unusual anterior and posterior segment features in patients affected by Coats disease.We identified therefore 4 unusual clinical conditions: retinal macrocysts, anterior chamber cholesterolosis, fovea-sparing Coats disease and secondary vasoproliferative tumor. RESULTS: Two patients presented with retinal macrocyst (2/45 = 4.4%), one with anterior chamber cholesterolosis (1/45 = 2.2%), two with fovea sparing Coats disease (2/45 = 4.4%) and one with vasoproliferative tumor associated (1/45 = 2.2%) for a total of six (6/45 = 13.3%) patients manifesting unusual anterior or posterior segment features in Coats disease. CONCLUSION: Unusual anterior and posterior segment features of Coats disease such as retinal macrocyst and anterior chamber cholesterolosis have been more frequently reported in younger children while fovea-sparing and vasoproliferative tumors have been more commonly described in older patients. Age is then a strong prognostic marker which allows to distinguish two different phenotypes of Coats disease: patients younger and older than 3 years old with more aggressive and milder phenotype respectively.

Rescue intra-arterial chemotherapy in unilateral multirelapsed peripapillary retinoblastoma: Decision making and the role of MRI.

INTRODUCTION: In this case report we report our experience with rescue intra-arterial chemotherapy in a case of multi-relapsed peripapillary Retinoblastoma (RB) and the importance of high resolution MRI in detecting possible optic disc infiltration. CASE REPORT: In 2007, a 14 month-old caucasian girl was referred to our ocular oncology unit for leukocoria. Only left eye was interested, with a single mass of the posterior pole. Patient underwent six cycles of systemic chemotherapy and focal laser consolidation. Several relapses occurred during follow-up. Selective intra-arterial chemotherapy (SIAC) with Melphalan was performed and type IV remission was achieved. A new relapse occurred next to the optic disc. MRI was performed and we decided to try to save the globe with a rescue cycle of SIAC. CONCLUSION: MRI has demonstrated to be useful in decision making in RB, giving us a last chance to save the globe.

Medulloepithelioma in newborn: Advanced clinical status.

We report three cases of congenital medulloepithelioma, which is an extremely rare clinical pattern of a tumor rare by definition. The aim of this study is to underline the clinical features of advanced medulloepithelioma in newborns.

Very late orbital recurrence of choroidal melanoma four decades post enucleation.

Orbital recurrence of malignant choroidal melanoma is quite uncommon, occurring in about 3% of patients undergoing enucleation for large tumors. Orbital recurrences after more than 10 years from enucleation are even rarer. In literature, only few reports described orbital recurrence that occurred between 10 and 40 years after primary diagnosis. Herein we report a very late choroidal melanoma recurrence, 40 years post enucleation, of a 52 year-old female who had undergone left enucleation at the age of 12. She presented to our clinic for consultation in 2017, complaining of difficulty to contain the prosthesis, as well as, presence of small pigmented palpable nodules inferiorly in her anophthalmic socket. The patient was not aware of the medical condition which had lead to the enucleation. We requested her medical reports and detailed history through her family. We realized after reviewing her charts 40 years back, that her enucleation was due to malignant choroidal melanoma (CMM). Full screening was performed. After magnetic resonance imaging (MRI), that showed the presence of nodular masses in the anophthalmic socket, an excisional biopsy was performed. Histopathology confirmed the diagnosis of CMM (epithelioid and spindle cell type), supporting the hypothesis that residual melanoma cells may remain clinically dormant for long periods, even for decades. A literature review was performed in order to review similar cases and to understand and discuss multiple factors, which may explain this extremely delayed recurrence. To the best of our knowledge, this is the third case to be reported in the literature.

13q Deletion Syndrome Involving RB1: Characterization of a New Minimal Critical Region for Psychomotor Delay.

Retinoblastoma (RB) is an ocular tumor of the pediatric age caused by biallelic inactivation of the RB1 gene (13q14). About 10% of cases are due to gross-sized molecular deletions. The deletions can involve the surrounding genes delineating a contiguous gene syndrome characterized by RB, developmental anomalies, and peculiar facial dysmorphisms. Overlapping deletions previously found by traditional and/or molecular cytogenetic analysis allowed to define some critical regions for intellectual disability (ID) and multiple congenital anomalies, with key candidate genes. In the present study, using array-CGH, we characterized seven new patients with interstitial 13q deletion involving RB1. Among these cases, three patients with medium or large 13q deletions did not present psychomotor delay. This allowed defining a minimal critical region for ID that excludes the previously suggested candidate genes (HTR2A, NUFIP1, PCDH8, and PCDH17). The region contains 36 genes including NBEA, which emerged as the candidate gene associated with developmental delay. In addition, MAB21L1, DCLK1, EXOSC8, and SPART haploinsufficiency might contribute to the observed impaired neurodevelopmental phenotype. In conclusion, this study adds important novelties to the 13q deletion syndrome, although further studies are needed to better characterize the contribution of different genes and to understand how the haploinsufficiency of this region can determine ID.

Retinoblastoma Is Characterized by a Cold, CD8+ Cell Poor, PD-L1- Microenvironment, Which Turns Into Hot, CD8+ Cell Rich, PD-L1+ After Chemotherapy.

Purpose: To investigate the impact of chemotherapy (CHT) on human retinoblastoma (RB) tumor microenvironment (TME). Cases and Methods: Ninety-four RBs were studied, including 44 primary RBs treated by upfront surgery (Group 1) and 50 primary RBs enucleated after CHT (CHT), either intra-arterial (IAC; Group 2, 33 cases) or systemic (S-CHT; Group 3, 17 cases). Conventional and multiplexed immunohistochemistry were performed to make quantitative comparisons among the three groups, for the following parameters: tumor-infiltrating inflammatory cells (TI-ICs); programmed cell death protein 1 (PD-1) positive TI-ICs; Ki67 proliferation index; gliosis; PD-1 ligand (PD-L1) protein expression; vessel number. We also correlated these TME factors with the presence of histological high-risk factors (HHRF+) and RB anaplasia grade (AG). Results: After CHT, a decrease in both RB burden and Ki67 positivity was observed. In parallel, most subsets of TI-ICs, PD-1+ TI-ICs, gliosis, and PD-L1 protein expression significantly increased (P < 0.001, P = 0.02, P < 0.001, respectively). Vessel number did not significantly vary. Age, HHRFs+ and AG were significantly different between primary and chemoreduced RBs (P < 0.001, P = 0.006, P = 0.001, respectively) and were correlated with most TME factors. Conclusions: CHT modulates host antitumor immunity by reorienting the RB TME from anergic into an active, CD8+, PD-L1+ hot state. Furthermore, some clinicopathological characteristics of RB correlate with several factors of TME. Our study adds data in favor of the possibility of a new therapeutic scenario in human RB.

Bilateral retinoblastoma and osteogenesis imperfecta, a very rare association: Two cases.

INTRODUCTION: This case report presents two patients affected by a very rare association of bilateral retinoblastoma and osteogenesis imperfecta. CASE REPORT: Two Caucasian males with familial history and clinical signs of osteogenesis imperfecta came to our attention for bilateral leukocoria. The ocular fundus examination revealed bilateral retinoblastoma. Proper therapies were dispensed in order to achieve full regression. Genetic counseling was performed. DISCUSSION: The primary role of genetics in retinoblastoma pathogenesis in widely known, and different genes have been identified. Osteogenesis imperfecta is a rare connective tissue disorders, caused by mutated genes encoding for collagen. The single gene defect in osteogenesis imperfecta type VI is Serpin Family F Member 1 (SERPINF1), a neurotrophic factor for the neuronal differentiation in retinoblastoma cells. The association of bilateral retinoblastoma and osteogenesis imperfecta could be the result of the mutation of a single gene playing a role in a hypothetical common pathway.

The Addition of Topotecan to Melphalan in the Treatment of Retinoblastoma with Intra-arterial Chemotherapy.

PURPOSE: To evaluate the effect of adding topotecan to melphalan for the treatment of retinoblastoma using intra-arterial chemotherapy (IAC). DESIGN: Single-center, consecutive case series. PARTICIPANTS: All eyes treated with IAC at the University of Siena, Siena, Italy, from 2008 to 2019. METHODS: Eyes were treated via IAC with either melphalan monotherapy or melphalan plus topotecan. The characteristics and outcomes of these 2 groups were compared. MAIN OUTCOME MEASURES: The main outcome measure was globe salvage rate. Additionally, a complete summary of all adverse events for all eyes was compared between groups and included local, regional, and systemic events causing both transient and permanent effects. RESULTS: A total of 193 patients and 208 eyes were treated with IAC between April 2008 and October 2019. Melphalan alone (MA) was used to treat 44 patients and 50 eyes for a total of 191 procedures. The combination of melphalan plus topotecan (MPT) was used to treat 149 patients and 158 eyes for a total of 780 procedures. Groups were similar in terms of age at presentation. The MPT group included more advanced eyes (P < 0.001) and had shorter follow-up time (mean 47 vs. 120 months in the MA group, P < 0.001). The MPT group required less laser and cryotherapy after treatment (32% of eyes vs. 50% of eyes in the MA group, P < 0.001); there was no other difference in the number of adjuvant treatments required between groups. There was no difference in the number of acute adverse events, both systemic and local, between groups. There was no difference in the number of transient or permanent intraocular side effects between groups. Kaplan-Meier survival analysis estimated a better globe salvage rate in the MPT group (66%) compared with the MA group (58%, P = 0.05). CONCLUSIONS: In this case series, the addition of topotecan to melphalan did not alter the IAC side effect profile and may contribute to improved globe salvage.

Fovea-sparing coats disease: A rare clinical entity.

PURPOSE: To evaluate the rarity, clinical features and management of Coats disease characterized by fovea-sparing enhancing the importance of pediatric retinal screening and early management to maintain a good visual acuity. METHODS: Retrospective analysis of approximately 40 patients affected by Coats disease between 2000 and 2020 at the Retinoblastoma Referral Center and Ophthalmology unit of the University of Siena in Italy. RESULTS: Two patients with fovea sparing Coats disease were included. Both presented an extrafoveal Coats disease (stage 2A by Shields classification) when they were 5 and 6 years old respectively.They had no anterior findings and a presenting visual acuity of 20/20 reflecting the early stage and a milder phenotype of the disease which are indeed more likely to be found in patients older than 3 years at presentation.Both presented telangiectasia and retinal exudation in the affected eye. Standard Argon laser photocoagulation and subsequently Cryotherapy were performed in the telangiectatic retinal periphery of both patients obtaining an excellent control and regression of the disease. CONCLUSIONS: Careful pediatric retinal screening and early management are crucial to ensure a good visual prognosis in such an early feature of Coats disease as fovea sparing since this condition unfortunately tends to recall the physician's attention in more advanced stages.Due to the extremely poor number of articles regarding such a rare feature of Coats disease like fovea sparing, we report our experience.

Orbital Pseudocellulitis: A Retinoblastoma-Associated Masquerade Syndrome.

INTRODUCTION: A masquerade syndrome is an atypical presentation of a neoplastic process that mimics an inflammatory condition. In this paper, we focus on orbital pseudocellulitis. CASE SERIES: Our case series includes 5 retinoblastoma patients with orbital pseudocellulitis at presentation. In 3 patients the disease was bilateral, in 1 trilateral, and in 1 unilateral. The eyes with pseudocellulitis were enucleated, while the fellow eyes were treated conservatively, when affected. Four patients responded well to the therapy and showed remission of the tumor. The patient with trilateral retinoblastoma did not respond to therapy and died of disease. DISCUSSION: Differential diagnosis with infectious orbital cellulitis is extremely important. Patients with orbital cellulitis present with fever, sinusitis, leukocytosis, and raised inflammatory markers, while ophthalmoscopic examination is negative and imaging studies show sinus involvement. On the contrary, patients with retinoblastoma do not show systemic inflammation, while ophthalmoscopic examination reveals leukocoria, buphthalmos, and an intraocular tumor mass associated with retinal detachment. Magnetic resonance imaging shows intralesional calcifications and soft tissue edema without sinus involvement. Histology confirms the diagnosis. CONCLUSIONS: Medical history, physical examination, and imaging studies are crucial in the diagnosis of retinoblastoma-associated orbital pseudocellulitis. Retinoblastoma should be excluded in all patients with signs of pre-septal orbital cellulitis through fundoscopy and/or imaging studies.

Intra-arterial chemotherapy for retinoblastoma: the dosimetric impact.

PURPOSE: Purposes are (1) to measure main radiation parameters and (2) to propose a method to estimate the absorbed doses of internal organs starting from DAP values. Measuring the exposition of internal organs by repeated irradiations on an anthropomorphic phantom with the same settings used in vivo, we could establish correlations between (1) DAP and the dose recorded by a dosimeter placed along the X-ray beam entrance pathway; (2) the dose recorded by the same dosimeter and the absorbed dose in internal organs. METHODS: Forty-four consecutive patients (16 males, 28 females) (mean age 35.4 months) treated at our institution with IAC (216 procedures: 196 via the ICA and 20 into branches of the ECA) were included in this prospective study. IAC was divided into 5 phases. Fluoroscopic time, DAP, and ESD were measured. RESULTS: The mean DAP was 595 ± 445 cGy cm2 and the mean fluoroscopic time was 540 ± 403 s. ESD was on average 9.59 mGy (range 0.8-165 mGy). The absorbed dose was lower than 12.1 mGy in the left retina (the more exposed organ) in 75% of single treatments and lower than 25 mGy in 95% of treatments. In the cases of 3 and 6 sessions, the left retina of 75% of patients absorbed respectively less than 36.3 and 72.7 mGy, whereas the left retina of 95% of patients received less than 75.2 and 150.4 mGy. Other organs were less exposed. CONCLUSION: This paper describes a method of absorbed dose estimation providing ranges used clinically in a single practice and the basis for further prospective studies.

Evidence of predisposing epimutation in retinoblastoma.

Retinoblastoma (RB), which represents the most common childhood eye cancer, is caused by biallelic inactivation of RB1 gene. Promoter hypermethylation is quite frequent in RB tissues but conclusive evidence of soma-wide predisposing epimutations is currently scant. Here, 50 patients who tested negative for RB1 germline sequence alterations were screened for aberrant promoter methylation using methylation-specific MLPA. The assay, performed on blood, identified a sporadic patient with methylation of CpG106, absent in parents' DNA. Bisulfite pyrosequencing accurately quantified CpG methylation in blood DNA (mean ∼49%) and also confirmed the aberration in DNA isolated from oral mucosa although at lower levels (mean ∼34%). Using a tag-SNP, methylation was demonstrated to affect the maternal allele. Real-time qPCR demonstrated RB1 transcriptional silencing. In conclusion, we documented that promoter methylation can act as the first "hit" in Knudson's model. This mosaic epimutation mimics the effect of an inactivating mutation and phenocopies RB onset.

Parent-of-origin effect of hypomorphic pathogenic variants and somatic mosaicism impact on phenotypic expression of retinoblastoma.

Retinoblastoma is the most common eye cancer in children. Numerous families have been described displaying reduced penetrance and expressivity. An extensive molecular characterization of seven families led us to characterize the two main mechanisms impacting on phenotypic expression, as follows: (i) mosaicism of amorphic pathogenic variants; and (ii) parent-of-origin-effect of hypomorphic pathogenic variants. Somatic mosaicism for RB1 splicing variants (c.1960+5G>C and c.2106+2T>C), leading to a complete loss of function was demonstrated by high-depth NGS in two families. In both cases, the healthy carrier parent (one with retinoma) showed a variant frequency lower than that expected for a heterozygous individual, indicating a 56-60% mosaicism level. Previous evidences of a ~3-fold excess of RB1 maternal canonical transcript led us to hypothesize that this differential allelic expression could influence phenotypic outcome in families at risk for RB onset. Accordingly, in five families, we identified a higher tumor risk associated with paternally inherited hypomorphic pathogenic variants, namely a deletion resulting in the loss of 37 amino acids at the N-terminus (c.608-16_608del), an exonic substitution with a "leaky" splicing effect (c.1331A>G), a partially deleterious substitution (c.1981C>T) and a truncating C-terminal variant (c.2663+2T>C). The identification of these mechanisms changes the genetic/prenatal counseling and the clinical management of families, indicating a higher recurrence risk when the hypomorphic pathogenic variant is inherited from the father, and suggesting the need for second tumor surveillance in unaffected carriers at risk of developing adult-onset cancer such as osteosarcoma or leiomyosarcoma.

Transorbital anastomotic pathways between the external and internal carotid systems in children affected by intraocular retinoblastoma.

PURPOSE: It is well known that many anastomoses can join the external carotid system and the ophthalmic artery. However, their frequency has never been reported. Since they can be relevant for interventional radiologists operating in the orbit, we decided to illustrate and determine the frequency of the anastomoses that can be found in children. METHODS: A retrospective study of 443 angiographic procedures (via ophthalmic artery and/or external carotid artery) carried out on 97 children affected by intraocular retinoblastoma was made to investigate the arterial anatomy of 106 orbits. RESULTS: Anastomoses were observed in 44.33 % of orbits. However, their true frequency is likely much higher as the rate of visualization increased up to 91.11 % of orbits when the angiographic study was extended to the external carotid artery. In order of frequency we detected the following anastomoses: lacrimal artery-middle meningeal artery, lacrimal artery-anterior deep temporal artery, ophthalmic artery-middle meningeal artery, ophthalmic artery-facial artery, supraorbital artery-superficial temporal artery, supratrochlear artery-superficial temporal artery, supraorbital artery-middle meningeal artery, dorsal nasal artery-infraorbital artery, supraorbital artery-zygomaticoorbital artery, lacrimal artery-zygomaticoorbital artery. CONCLUSION: When properly searched, anastomoses between the ophthalmic artery and the external carotid artery are almost constant in children. Depending on the clinical scenario, they can represent dangers or valuable alternative routes for collateral circulations and intraarterial chemotherapy.

Diagnostic Accuracy of Intraocular Tumor Size Measured with MR Imaging in the Prediction of Postlaminar Optic Nerve Invasion and Massive Choroidal Invasion of Retinoblastoma.

Purpose To assess the correlation of intraocular retinoblastoma tumor size measured with magnetic resonance (MR) imaging in the prediction of histopathologically determined metastatic risk factors (postlaminar optic nerve invasion and massive choroidal invasion). Materials and Methods The ethics committee approved this retrospective multicenter study with a waiver of informed consent. The study population included 370 consecutive patients with retinoblastoma (375 eyes) who underwent baseline MR imaging, followed by primary enucleation from 1993 through 2014. Tumor sizes (maximum diameter and volume) were measured independently by two observers and correlated with histopathologic risk factors. Receiver operating characteristic curves were used to analyze the diagnostic accuracy of tumor size, and areas under the curve were calculated. Logistic regression analysis was performed to evaluate potential confounders. Results Receiver operating characteristic analysis of volume and diameter, respectively, yielded areas under the curve of 0.77 (95% confidence interval [CI]: 0.70, 0.85; P < .0001) and 0.78 (95% CI: 0.71, 0.85; P < .0001) for postlaminar optic nerve invasion (n = 375) and 0.67 (95% CI: 0.57, 0.77; P = .0020) and 0.70 (95% CI: 0.59, 0.80; P = .0004) for massive choroidal tumor invasion (n = 219). For the detection of co-occurring massive choroidal invasion and postlaminar optic nerve invasion (n = 219), volume and diameter showed areas under the curve of 0.81 (95% CI: 0.70, 0.91; P = .0032) and 0.83 (95% CI: 0.73, 0.93; P = .0016), respectively. Conclusion Intraocular tumor size shows a strong association with postlaminar optic nerve invasion and a moderate association with massive choroidal invasion. These findings provide diagnostic accuracy measures at different size cutoff levels, which could potentially be useful in a clinical setting, especially within the scope of the increasing use of eye-salvage treatment strategies. (©) RSNA, 2015 Online supplemental material is available for this article.

Alternated intra-arterial and intravitreal chemotherapy for advanced intraocular retinoblastoma: preliminary successful results without systemic chemotherapy.

To describe the efficacy of intravitreal chemotherapy (IViC) preceded by intra-arterial chemotherapy (IAC) for the treatment of advanced stage retinoblastoma. This non-comparative interventional case series retrospectively reviewed the medical records of six patients who presented within months of each other with unilateral retinoblastoma, Reese-Ellsworth stage Vb/D of ABC classification in the affected eye. After clinical and ophthalmoscopic evaluation, they underwent MRI to exclude local and CNS dissemination. The IAC was given to treat retinal masses and intravitreal injections to treat vitreous seeding. Patients had received two cycles (six infusions) of IAC, and from six up to ten melphalan injections into the vitreous, with an interval of 7-10 days between them. From one to four intravitreal injections were performed for partial remission or consolidation. No permanent complications of procedures have been reported. All patients underwent to bimonthly MRI examination, during treatment and every 3 months for 1 year after last injection, to exclude orbital dissemination. Successful control (100 %) of tumor masses and vitreous seeds was achieved in all cases at 12 months follow-up. Complications were posterior lens opacity, acute ischemic papillitis, partial CVR thrombosis, hypotonia (case 1), partial vitreous hemorrhage (case 4). No complications appeared in cases 2, 3, 5, and 6. No intraocular or orbital tumor recurrence or retinoblastoma metastases (follow-up range, 12-33 months) were observed. Sequential IAC and intravitreal melphalan for advanced retinoblastoma allowed to provide retinal and vitreous seed control.

Identification of Intraorbital Arteries in Pediatric Age by High Resolution Superselective Angiography.

PURPOSE: Angiography is a powerful tool to identify intraorbital arteries. However, the incidence by which these vessels can be identified is unknown. Our purpose was to determine such incidence and which angiographic approach is best for the identification of each artery. METHODS: A retrospective study of 353 angiographic procedures (via ophthalmic artery and/or external carotid artery) carried out on 79 children affected by intraocular retinoblastoma was made to investigate the arterial anatomy in 87 orbits. For each intraorbital artery two parameters were calculated: the angiographic incidence, as the percentage of times a given artery was identified, and the visibility index, as the ratio between the angiographic incidence and the true anatomic incidence. RESULTS: All collaterals of the ophthalmic artery could be spotted. Most of them were identified with a high angiographic incidence; some of them were less easily identified because too thin or because frequently shielded. The visibility index paralleled the angiographic incidence of most arteries. However, the lacrimal and meningolacrimal arteries had a higher visibility index suggesting that their identification was more frequent than the angiographic incidence alone could suggest. Statistical analysis demonstrated that the lacrimal artery and some muscular branches had higher chances to be identified if the angiography of the ophthalmic artery was accompanied by the study of the external carotid system. CONCLUSION: This work provides an objective measure of how powerful angiography is to identify intraorbital arteries as well as useful references for professionals who need to operate in the orbit.

MRI helps depict clinically undetectable risk factors in advanced stage retinoblastomas.

This study compared high-resolution MRI with histology in advanced stage retinoblastomas in which ophthalmoscopy and ultrasonography did not give an exhaustive depiction of the tumour and/or its extension. MRI of orbits and head in 28 retinoblastoma patients (28 eyes) treated with primary enucleation were evaluated. Iris neoangiogenesis, infiltrations of optic nerve, choroid, anterior segment and sclera suspected at MR and histology were compared. Abnormal anterior segment enhancement (AASE) was also correlated with histologically proven infiltrations. Brain images were also evaluated. Significant values were obtained for: prelaminar optic nerve (ON) sensitivity (0.88), positive predictive value (PPV) (0.75) and negative predictive value (NPV) (0.71); post-laminar ON sensitivity (0.50), specificity (0.83), PPV (0.50) and NPV (0.83); overall choroid sensitivity (0.82), and massive choroid NPV (0.69); scleral specificity (1), and NPV (1). AASE correlated with iris neoangiogenesis in 14 out of 19 eyes, and showed significant values for: overall ON PPV (0.65), prelaminar ON sensitivity (0.65), and PPV (0.61), post-laminar ON NPV (0.64); overall choroid sensitivity (0.77), PPV (0.59) and NPV (0.73); scleral NPV (0.83); anterior segment sensitivity (1), and NPV (1). Odds ratios (OR) and accuracy were significant in scleral and prelaminar optic nerve infiltration. Brain examination was unremarkable in all cases. High-resolution MRI may add important findings to clinical evaluation of advanced stage retinoblastomas.

Next generation sequencing in sporadic retinoblastoma patients reveals somatic mosaicism.

In about 50% of sporadic cases of retinoblastoma, no constitutive RB1 mutations are detected by conventional methods. However, recent research suggests that, at least in some of these cases, there is somatic mosaicism with respect to RB1 normal and mutant alleles. The increased availability of next generation sequencing improves our ability to detect the exact percentage of patients with mosaicism. Using this technology, we re-tested a series of 40 patients with sporadic retinoblastoma: 10 of them had been previously classified as constitutional heterozygotes, whereas in 30 no RB1 mutations had been found in lymphocytes. In 3 of these 30 patients, we have now identified low-level mosaic variants, varying in frequency between 8 and 24%. In 7 out of the 10 cases previously classified as heterozygous from testing blood cells, we were able to test additional tissues (ocular tissues, urine and/or oral mucosa): in three of them, next generation sequencing has revealed mosaicism. Present results thus confirm that a significant fraction (6/40; 15%) of sporadic retinoblastoma cases are due to postzygotic events and that deep sequencing is an efficient method to unambiguously distinguish mosaics. Re-testing of retinoblastoma patients through next generation sequencing can thus provide new information that may have important implications with respect to genetic counseling and family care.