With the availability of high-sensitivity molecular genetic testing, prenatal diagnosis by amniocentesis, early-term delivery of at-risk neonates, and hand-held optical coherence tomography for detection of subclinical tumors, there is an opportunity to optimize eye and vision salvage and minimize the burden of invasive treatments in hereditary retinoblastoma. Providing this standard of care requires consistent practice patterns and collaboration between diagnostic laboratories and tertiary retinoblastoma centers. We describe two cases that highlight the importance of timely and accurate RB1 genetic testing and identification and clinical evaluation of at-risk family members, to optimize outcomes for individuals with hereditary retinoblastoma.

Retinoblastoma is the most common intraocular tumor of childhood. In Lebanon, its incidence is reported at 3.6 per million person-years. This study aimed to characterize the spectrum of RB1 variants in hereditary retinoblastoma and explore genotype-phenotype associations in a Lebanese cohort. A retrospective chart review was conducted on retinoblastoma patients enrolled in the Children's Cancer Institute at the American University of Beirut Medical Center from 2012 to 2022. Genetic data (RB1 sequencing and karyotype), clinical characteristics, imaging, treatment, and outcomes were collected and compared between hereditary and sporadic cases, and across different variant types. A total of 47 patients underwent genetic testing; 63% had hereditary retinoblastoma with 23 patients carrying single nucleotide changes, including four novel mutations, 3 patients with submicroscopic deletions/duplications, and 3 with deletion 13q syndrome. Nonsense mutations were most frequent (52.2%), followed by frameshift and splice-site alterations. Bilaterality was significantly associated with hereditary disease (85.7% vs. 21.1%, p < 0.001), and more common among Syrian patients (p = 0.04). Median age at diagnosis was younger in the hereditary group, although not statistically significant. Enucleation rates (57.1% vs. 78.9%) and vision outcomes were similar across groups (p > 0.05). No significant differences in treatment outcomes were found among different variant types. Among the 3 patients with deletion 13q, two exhibited severe psychomotor and developmental delays. Hereditary retinoblastoma accounted for 63% of cases, with 23 pathogenic variants including four novel ones. Bilaterality and Syrian nationality were significantly associated with RB1 positivity. This study underscores the importance of comprehensive RB1 genetic testing in improving diagnostic accuracy, guiding treatment decisions, and supporting genetic counselling, particularly in non-Western populations.

Retinoblastoma (RB) is the most common primary intraocular malignancy in children and mostly initiates with biallelic inactivation of the RB1 gene. Hereditary retinoblastoma accounts for 40% of all cases, with only 6%-10% of patients having a positive family history. The proband, a Chinese Tibetan boy, was diagnosed with RB for leukocoria. The RB1 gene mutations were screened due to disease recurrence. A novel germline donor splicing site mutation (c.861 + 2T>A) from his father was identified by Sanger sequencing and a novel somatic duplication mutation in exon 2 221-224 (p.W75Cfs*36) by next-generation sequencing (NGS). The proband's younger brother manifested bilateral RB and also carried the same germline mutation. To further explore the possible pathogenicity of the novel germline RB1 mutation (c.861 + 2T>A) in RB development, mutation analysis, bioinformatics analysis, and immunohistochemistry were performed. After RB1 cDNA was amplified, the abnormal script was found to be smaller than the normal script. Compared with normal samples, Sanger sequencing revealed a deletion of 143 bp in the abnormal script. In comparison to healthy individuals, patients exhibited a reduction in the mRNA expression levels of the RB1 gene. The three-dimensional structure predicted by iterative threading assembly refinement (I-TASSER) indicates significant changes in the spatial structure of abnormal proteins after mutation. No expression of RB1 was found in tumor tissue by immunohistochemistry evaluation. Therefore, the novel germline donor splicing site mutation (c.861 + 2T>A) has been confirmed to be a pathological mutation.

Retinoblastoma, the primary ocular tumor in childhood, arises from the photoreceptor cells of the retina caused by pathogenic loss-of-function variants in both alleles of the RB1 gene, which can be either germline or somatic. The predisposition to hereditary retinoblastoma is primarily linked to germline variants in the RB1 gene. Here, we describe a two-year-old girl from a Mennonite community who presented at 6 months of age with unilateral Group E retinoblastoma and underwent enucleation. She had a strong family history of cancer: a third elder sister deceased at age 4 with concurrent Burkitt lymphoma and medulloblastoma, and father diagnosed with carcinoid tumor at age 27. RB1 gene testing detected two pathogenic variants in the RB1 gene (c.299dup, c.1959del) in the tumor tissue. These variants were not identified in blood, indicating somatic changes. Testing of 49 genes associated with cancer predisposition identified a germline homozygous likely pathogenic variant in PMS2 (c.2095 G>T, p.Asp699His) in the proband, consistent with the diagnosis of constitutional mismatch repair deficiency (CMMRD). The proband's fourth elder sister who also tested homozygous for the PMS2 variant, was diagnosed with low grade glioma identified during screening as a part of surveillance for CMMRD. This case highlights the importance of considering CMMRD in retinoblastoma with normal germline RB1 sequence, particularly with additional factors like family cancer history, consanguinity, or multiple childhood malignancies. Given retinoblastoma's association with CMMRD, screening for it in children with CMMRD is recommended.

Survivors of hereditary retinoblastoma have increased risk of subsequent primary malignancies due to RB1 mutation. We report uterine leiomyosarcoma (LMS) in a hereditary retinoblastoma survivor. She had follow-up for leiomyomas, with pelvic MRI showing typical leiomyomas two years prior. She presented with abdominal distention, and MRI revealed a massive tumor with LMS characteristics where a leiomyoma was previously observed. Chest CT showed a nodule suspicious for metastasis in the left lung. Total hysterectomy with bilateral salpingo-oophorectomy and partial lung resection was performed. Pathology confirmed LMS with pulmonary metastasis. Immunostaining showed complete RB1 loss in tumor cells. LMS was suspected to have arisen near a pre-existing leiomyoma or resulted from its malignant transformation. Continuous follow-up is necessary in hereditary retinoblastoma survivors.