BARD1 germline pathogenic variants (gPV) have been primarily associated with moderate breast cancer risk but their rarity limits accurate risk assessment and tailored follow-up guidelines. Our study evaluates the association between BARD1 gPV and breast cancer while exploring the role of BARD1 in mammary oncogenesis. In this case-control study, 7,309 women with breast cancer and no gPV identified in the French hereditary breast and ovarian cancer (HBOC) gene panel at the Institut Curie were compared to 57,681 female controls from the gnomAD European non-cancer database. Tumors were analyzed for biallelic BARD1 inactivation and homologous recombination deficiency (HRD). A significant association was observed between BARD1 gPV and breast cancer (OR = 5.2, 95

Background. DICER1 syndrome is an autosomal dominant disorder predisposing to a broad spectrum of malignant and benign neoplasms, caused by germline pathogenic variants (PVs) in the DICER1 gene. We aimed to characterize the clinical features of DICER1 syndrome in a national referral cohort and to estimate neoplasm risk.Materials and Methods. This retrospective study was conducted in a cohort of 945 patients who underwent DICER1 genetic testing at Institut Curie, Paris, using Sanger sequencing from 2012 to 2014 and Next Generation Sequencing from 2015 to 2023.Results. Among 584 index cases evaluated for DICER1 syndrome, 91 (16%) carried a germline DICER1 PV and 31 (5%) harbored only somatic DICER1 PVs. Several tumors that were not previously part of the DICER1 tumor spectrum were identified. ETMR-like brain tumor and testicular Sertoli cell tumor are now recognized as DICER1-related neoplasms, and schwannoma is a strong candidate. The neoplasm risk was estimated in 170 relatives carrying a germline DICER1 PV. The cumulative incidence of malignant neoplasms was 4.8% [95% CI: 2.1% – 9.1%] at 10 years and 15.8% [95% CI: 8.9% – 24.7%] at 50 years. Overall neoplasm risk was significantly higher in females, primarily driven by the higher incidence of multinodular goiter.Conclusion. This large cohort study provides a comprehensive overview of the distribution of neoplasms associated with DICER1 syndrome. Broader genetic testing identified additional DICER1-related neoplasms, and schwannoma emerged as a candidate association. Finally, this study confirms the moderate penetrance of germline DICER1 PVs.

TP53 is included in most cancer predisposition multigene panels, especially those exploring Hereditary Breast and Ovarian Cancer (HBOC) predisposition. The purpose of this study was to define the contribution of TP53 pathogenic variants (PV) to the HBOC phenotype by collecting genotypes and phenotypes of 398 patients harboring a TP53 variant identified by 53,085 HBOC panel sequencing in 15 French laboratories. Heterozygous TP53 variants were identified in 0.44% of HBOC panels, evenly distributed between PV and VUS. Breast cancers associated with TP53 were predominantly triple positive, particularly Her2+ breast cancer, in situ cancer, or phyllodes tumors ( p < 0.0001 for both). Interestingly, TP53 PV were identified across all ages in breast cancer patients, with enrichment before 36y. We demonstrated that null variants were linked with the HBOC phenotype, and missense variants, especially with a dominant negative effect, with the LFS phenotype ( p = 0.0096). Patients with breast cancer harboring null variants displayed an earlier age of onset compared to missense ( p = 0.0030). Surprisingly, we identified, in late‐onset cancer patients, TP53 hotspot PV usually identified in classic LFS, which underlines variable penetrance. Thus, this study suggests the existence of two phenotypic entities associated with TP53 PV: clinical LFS and TP53 ‐related breast cancer. The type of TP53 variant, as well as modifying factors reflected in family history, may influence these phenotypes, and both should be considered to define the clinical follow‐up of patients and relatives.

BACKGROUND:Lynch syndrome is an autosomal dominant cancer predisposition syndrome classically caused by germline mutations of the mismatch repair genes MLH1, MSH2, MSH6 and PMS2. Epimutation (also called germline hypermethylation) of the MLH1 gene promoter explains rare Lynch syndrome cases. To date, there is no recommendation regarding the techniques to be used to detect this epimutation, nor any clinical criteria for when it should be investigated. We present a retrospective study involving 73 patients whose Lynch syndrome-related tumours exhibited MLH1 hypermethylation, and compare the methylation-sensitive high-resolution melting (MS-HRM) technology to the gold standard method of pyrosequencing, in view of performing routine MLH1 epimutation testing. We further ascertained epimutation of MLH1 by MS-HRM from a control group of 25 patients with known MMR germline pathogenic variant. RESULTS:MLH1 epimutation was detected in 6.8% of the comprehensive cohort (5/73). MS-HRM detected one positive case previously identified by pyrosequencing, along with two missed cases at very low allelic frequencies and allowed the identification of two additional positive patients, subsequently confirmed by pyrosequencing. No patients in the control group were found to have MLH1 epimutation. CONCLUSION:MS-HRM is a simple and sensitive real-time PCR method amenable to routinely detect MLH1 epimutation, with high sensitivity. Identifying patients with MLH1 epimutation is of paramount importance for patient care and genetic counselling. We further recommend performing this analysis systematically in discrete clinical settings herewith specified.

Uveal melanoma (UM) is the most common intraocular malignancy in adults. Thus far, germline mutations of two genes have been identified to be predisposing to UM with a high penetrance: BAP1, responsible for the BAP1 tumor predisposition syndrome (BAP1-TPDS), and MBD4, which germline alterations are associated with tumor predisposition, specific tumor mutational signature and response to immunotherapy. However, only a fraction of familial and bilateral/multifocal forms of UM can be explained by these germline alterations, suggesting the existence of other predisposing factors. We analyzed a panel of 122 candidate cancer predisposing genes by target sequencing on germline DNA from a prospective unbiased cohort of 381 patients diagnosed with UM at Institut Curie between July 2021 and February 2023. We identified 29 pathogenic variants (PVs) in genes that are relevant for patient monitoring and genetic counselling (6 in MBD4, 3 in BAP1, 3 in BRCA2, 1 in ATM, 3 in FAN1, 2 in FANCL, 3 in FANCM, 1 in MLH1, 1 in MSH2, 2 in MSH6 and 4 in PMS2). Two patients had PVs in MSH6, 4 in PMS2, 1 in MLH1 and 1 in MSH2. The frequencies of the 3 MisMatch Repair (MMR) genes MLH1, MSH2 and MSH6 were significantly higher than in the gnomAD (v2.1.1) non-Finnish European database as a matched control sub-cohort (p=0.00073, OR: 10.4 [2.8-27.5]). PMS2 was excluded from this statistical analysis because its pseudogene prevents the interpretation of public data. One UM tumor sample was further characterized from the patient carrying the germline MLH1 PV. This UM displayed biallelic inactivation of MLH1, loss of MLH1 and PMS2 expression by immuno-histochemistry, a prominent Substitution Mutational Signature 6 (SBS6) associated with MMR deficiency from whole Genome Sequencing (WGS) and an MSI-H phenotype. This study confirms MMR genes as predisposing factors in UM, as suggested by two previous case reports identifying MLH1 germline PVs and biallelic inactivation in UM cases (Lobo et al. Virchows Arch 2017;470:347; Abdel-Rahman et al. Ophthalmology 2020;127:668). Further analyses will be needed to define the risk of developing UM for patients with a Lynch syndrome. Marc-Henri Stern, Anaïs Le Ven, Marie-Charlotte Villy, André B. Silveira, Alexandre Houy, Mathilde Warcoin, Marine Le Mentec, Fatoumata Simaga, Antoine De Pauw, Bruno Buecher, Marion Gauthier-Villars, Thibault Verrier, Kevin Merchadou, Victor Renault, Anne Vincent-Salomon, Juliette Sauge, Sophie El Zein, Catherine Dubois d’Enghien, Sophie Piperno-Neumann, Alexandre Matet, Denis Malaise, Nathalie Cassoux, Livia Lumbroso-Le Rouic, Dominique Stoppa-Lyonnet, Manuel R. Rodrigues, Lisa Golmard, Chrystelle Colas. A prospective analysis identified mismatch repair genes as predisposing for uveal melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4906.

Alterations of PHOX2B function is associated with a wide range of diseases, including congenital central hypoventilation syndrome (CCHS) and neural crest-derived tumors, from low-grade (ganglioneuromas) to malignant forms (neuroblastomas). We report a case bearing a novel nonpolyalanine repeat PHOX2B pathogenic variant presenting both as high-risk neuroblastoma and late-onset CCHS. CCHS was revealed upon severe respiratory decompensation while the patient was administered the anti-GD2 antibody dinutuximab-beta, as part of neuroblastoma treatment. From this experience, we make propositions for the management of patients with high-risk neuroblastoma and a constitutional pathogenic variant of PHOX2B .

Bone sarcomas, constituting less than 1% of malignant neoplasms across all age groups, are rare tumours possibly associated with genetic susceptibility syndromes. This review aims to provide recommendations for the detection of cancer predisposition syndromes associated with bone sarcomas and managing affected patients. Recommendations were formulated by a multidisciplinary working and reviewing group from GroupOs and SFCE oncogenetic's group, including geneticists, oncologists, and radiologists. For various bone sarcomas including osteosarcomas, chondrosarcomas and Ewing sarcomas, we delineate tumour presentation, management strategies, and follow-up within the context of cancer predisposition syndromes. The inherited predisposition syndrome, associated with germline TP53 variants, known as the Li-Fraumeni syndrome, is the most frequent implicated in osteosarcoma cases. Other cancer predisposition syndromes, such as RB1, RECQ or CDKN2A disorders in osteosarcomas and Ollier and Maffucci diseases in chondrosarcomas, are also recognized. Additionally, we discuss rarer cancer predisposition syndromes associated with bone sarcomas and suggest tailored treatment approaches in some cancer predisposition syndromes to mitigate severe toxicities or secondary oncological events. Furthermore, we emphasize the role of identification somatic molecular variations in identifying constitutional germline variants and describe national and international screening programs, reference networks and molecular tumour boards available for collegial and collaborative management discussion. This comprehensive review provides insights into the intricate interplay between genetic predisposition, tumour biology, and therapeutic interventions in bone sarcoma patients with cancer predisposition syndrome.

PURPOSE:The RB1 gene encodes the retinoblastoma protein (pRB) playing a major role in cell cycle control, particularly by its interaction with E2F transcription factors. Familial forms of retinoblastoma are caused by germline pathogenic variants in the RB1 gene predisposing to retinoblastoma and other tumors. By analyzing the RB1 gene in patients with retinoblastoma, we found that missense variants often remain variants of uncertain significance (VUS). METHODS:To classify RB1 VUS, we developed a functional assay evaluating their impact on the ability of pRB to inhibit the activity of the E2F1 promoter, with a luciferase reporter gene. A set of 14 pathogenic/likely pathogenic and benign/likely benign RB1 variants was used for validation. RESULTS:We tested 16 VUS detected in patients with retinoblastoma and found that 9 VUS reduced the ability of pRB to inhibit E2F1 promoter. Among them, the (RB1) c.2263T>G p.(Phe755Val) variant showed a reduced level of pRB on Western blot, suggesting a defect in pRB stability. By applying the criterion PS3_moderate of the American College of Medical Genetics and Genomics/Association for Molecular Pathology classification to this functional assay, 5 of the 9 VUS with functional impact could be classified as likely pathogenic. CONCLUSION:This functional assay can improve the molecular diagnosis of retinoblastoma predisposition by a better determination of pathogenic/likely pathogenic RB1 variants.

Rhabdoid tumours (RT) are an aggressive malignancy affecting <2-year-old infants, characterised by biallelic loss-of-function alterations in SWI/SNF-related BAF chromatin remodelling complex subunit B1 (SMARCB1) in nearly all cases. Germline SMARCB1 alterations are found in similar to 30% of patients and define the RT Predisposition Syndrome type 1 (RTPS1). Uveal melanoma (UVM), the most common primary intraocular cancer in adults, does not harbour SMARCB1 alterations. We report two cases of a previously undescribed intraocular malignancy that shared some features with UVM and RT, but was also distinct from these entities. Both female patients, aged 23 and 14 years, underwent enucleation, and the tumours were subjected to comprehensive genomic, DNA methylation, and transcriptomic profiling. Pathological examination showed large, amelanotic intraocular tumours with epithelioid features, expressing melanocytic markers [S100P, SOX10, Melan-A, PMEL (HMB45), TYR] as seen using immunohistochemistry (IHC), but with little or no melanin production. Both tumours harboured biallelic loss-of-function SMARCB1 alterations, associated with loss of SMARCB1 (BAF47/INI1) expression on IHC. Their genomic profiles were atypical both for UVM and for RT, and no pathogenic variants were found in other genes tested, including those recurrently altered in UVM. In both patients, a germline SMARCB1 variant was found. However, there was no relevant family history of cancer. Transcriptome and methylome profiling suggested that these tumours were distinct from RT, UVM, and skin melanomas. RNAseq confirmed expression of early and late genes related to melanocytic differentiation. The first patient died of metastatic disease 16 months after diagnosis, the second was disease-free 10 months after completion of treatment. In summary, we report two cases of a previously undescribed, aggressive SMARCB1-deficient intraocular malignancy with melanocytic differentiation, which occurs in young patients, is distinct from UVM and RT, and expands the RTPS1 spectrum. (c) 2025 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

The access to next-generation sequencing, primarily performed for therapeutic purposes, has considerably increased in the real-time clinical practice in pediatric malignancies. Using germline DNA as a matched reference, this approach is also a unique opportunity to detect alterations in medically actionable genes (named "additional data"). The main objective of this project was to estimate the frequency of such genetic predisposition discoveries among children and adolescents with relapsing or refractory cancer. Among 791 children included in MAPPYACTS “MoleculAr Profiling for Pediatric and Young Adult Cancer Treatment Stratification” study, germline DNA exome sequencing was available for 674 patients with many distinct cancer types. Informed consent was obtained to disclose genetic findings if an actionable predisposition was detected. A multidisciplinary germline molecular board established the list of genes to be looked at, including 184 cancer predisposition genes with consensual surveillance guidelines, and 49 non cancer genes belonging to the ACMG Secondary Findings v3.1 list. Bioinformatic analysis included two different indel variant calling (Varscan and Haplotypecaller), quality controls and filters to ensure high-confidence variant calls, ClinVar annotations for pathological classification and in-silico function assessment by computational prediction (with several tools including CADD, SpliceAI and SPiP). Expert biologists have evaluated the pathogenicity of genetic variations with the use of genetic databases, computational predictions and medical literature. Among 184 cancer genes, 16 607 genetic variants have emerged. Twenty-five per cent of them were classified as unknown significance corresponding to a median of 7 (0;47) variants/patient and 8% of variants were retained as likely pathogenic or pathogenic variant (LPV/PV). Thus, 132 patients (19.6%) carried one LPV/PV variant among 53 cancer genes. According to inheritance patterns (we retained heterozygous variant for dominant disease and only biallelic events for recessive disease), genetic counselling was recommended for 58 patients (8.6%). Only two patients had two different cancer predisposition. The most frequently involved genes were TP53 (n=16), DICER1 (n=5), NF1 (n=4) and BRCA1 (n=4). Those identified genetic predispositions to cancer corresponded to the expected tumor spectrum in 50% of cases and were previously known in 38% of families. Furthermore, 10 patients (1.5%) were germline carriers of LPV/PV in genes involved in other genetic conditions (n=6 for cardiopathy; n=2 familial hypercholesterolemia; n=2 transthyretin amyloidosis). A specific evaluation of exome sequenced for therapeutic purposes provides germline information that could be actionable for 10.1% of families to improve cancer prevention or manage some other genetic condition. The psychological impact induced by the return of secondary findings to families will be investigated. Tiphaine Adam de Beaumais, Yahia Adnani, Léa Guerrini-Rousseau, Samuel Abbou, Cécile Acquaviva-Bourdain, Pablo Berlanga, Adeline Bonnard, Gaelle Bougeard, Franck Bourdeaut, Nelly Burnichon, Sandrine Caputo, Alain Carrié, Olivier Caron, Hélène Cavé, Albain Chansavang, Nadège Corradini, Sophie Cotteret, Philippe Denizeau, Alice Fievet, Mathilde Filser, Marion Gauthier-Villars, Birgit Geoerger, Nadim Hamzaoui, Edwige Kasper, Florence Kyndt, Ludovic Lacroix, Jessica Le Gall, Julien Masliah-Planchon, Laurence Pacot, Cécile Pagan, Mélanie Pagès, Béatrice Parfait, Eric Pasmant, Gaelle Pierron, Pascale Richard, Nathalie Roux-Buisson, Cécile Saint-Martin, Hela Sassi, Gudrun Schleiermacher, Renaud Touraine, Nancy Uhrhammer, Dominique Vidaud, Laurence Brugières, Gilles Vassal, Etienne Rouleau, Yoann Vial, Lisa Golmard, Odile Cabaret. Genetic predisposition discoveries of clinical utility by exome sequencing performed for therapeutic purposes in children with relapsing or refractory cancer in the MAPPYACTS study [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Discovery and Innovation in Pediatric Cancer— From Biology to Breakthrough Therapies; 2025 Sep 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl_2):Abstract nr A006.

Background: Women with a familial predisposition to breast cancer (BC) are offered screening at earlier ages and more frequently than women from the general population. Methods: We evaluated the effect of screening mammography in 1552 BC cases with a hereditary predisposition to BC unexplained by BRCA1 or BRCA2 and 1363 unrelated controls. Participants reported their lifetime mammography exposures in a detailed questionnaire. Germline rare deleterious or predicted deleterious variants (D-PDVs) in 113 DNA repair genes were investigated in 82.5% of the women and classified according to the strength of their association with BC. Genes with an odds ratio (OR) < 0.9 was assigned to the Gene Group “Reduced”, those with OR ≥ 0.9 and ≤1.1 to Group “Independent”, and those with OR > 1.1 to Group “Increased”. Results: Overall, having been exposed to mammograms (never vs. ever) was not associated with BC risk. However, an increase in BC risk of 4% (95% CI: 1–6%) per additional exposure was found under the assumption of linearity. When grouped according to D-PDV carrier status, mammograms doubled the BC risk of women carrying a D-PDV in Group “Reduced”, as compared to those carrying a D-PDV in Group “Increased”. Conclusions: Our study is the first to investigate the joint effect of mammogram exposure and variants in DNA repair genes other than BRCA1 and BRCA2 in women at high risk of BC; therefore, further studies are needed to verify our findings. Even though mammographic screening reduces the risk of mortality from BC, the identification of populations that are more or less susceptible to ionizing radiation may be clinically relevant.

Introduction:Retinocytomas are rare benign intraocular tumors that may mimic spontaneously regressed retinoblastoma (Rb). Materials and Methods:This was a retrospective monocentric study of patients with retinocytoma in a French tertiary ocular oncology center, with an inclusion period from January 1999 to January 2024. Results:Sixteen patients with retinocytoma were identified, and 1,351 Rbs were diagnosed during the same 25-year period. Age at diagnosis ranged from 11 months to 75 years (mean 28.1 years). Thirteen cases were asymptomatic, while three presented with floaters, decreased visual acuity, or strabismus. Clinical presentation was a whitish or grayish retinal tumor with a translucent (87%) and/or fragmented appearance (76%) at diagnosis. A proportion of lesions were surrounded by atrophy (52%) and/or pigmentation (30%). Eleven patients had unilateral retinocytoma (one of which was multifocal), and five had bilateral lesions. Eight patients had a known family history of Rb. Patients were followed regularly and underwent genetic counseling. The eight patients with a family history had a germline pathogenic variation of the RB1 gene. None showed malignant transformation during follow-up (mean 79.5 months, median 35.5 months). Conclusion:The presentation of retinocytoma is most often asymptomatic. Thus, diagnosis may be delayed to far later ages than expected with Rb. Retinocytoma may be associated with germline pathogenic variants of the RB1 gene, and follow-up is recommended due to rare but possible malignant transformation.

Importance:To date, no environmental factors and few therapeutic options are known for uveal melanoma (UM), the most common malignant intraocular primary tumor in adults. Identification of new predisposition factors could lead to better monitoring and possibly improved treatments of patients with UM. Objective:To identify new genetic alterations predisposing for UM. Design, Setting, and Participants:This was a prospective cohort study conducted at Institut Curie in Paris, France, among 381 consecutive patients diagnosed with UM between July 2021 and February 2023. UM was diagnosed clinically by ophthalmologists, and a senior pathologist confirmed the diagnosis when tumor or biopsy was available. All participants received genetic counseling and consented to extended genetic testing. A panel of 122 genes predisposing to cancer were analyzed by targeted sequencing on germline DNA from these patients. Main Outcomes and Measures:Frequency of pathogenic variants (PVs) in genes from a targeted panel, with classification of germline PVs done according to the American College of Medical Genetics and Genomics guidelines and the French Unicancer Genetics Group. Results:A total of 79 PVs were identified in 70 participants (41 female and 29 male; mean [SD] age, 60.6 [15.3] years). Among them, 21 were found in clinically relevant genes, with an enrichment in the mismatch repair (MMR) genes, involved in Lynch syndrome, a frequent predisposition to colon and endometrial cancers. This finding suggested MMR germline PVs could also predispose to UM. One tumor was available from a participant carrying a MLH1 germline PV. The tumor exhibited a monosomy 3 with loss of the wild-type allele of MLH1, located on chromosome 3. Loss of expression of MLH1 was observed by immunohistochemistry, and MMR variant signatures SBS6, ID1, and ID2 were identified from the whole-genome sequencing of this tumor, supporting the possibility that MLH1 contributes to the oncogenesis of this UM. Conclusions and Relevance:This prospective germline study on patients with UM provided evidence supporting the notion that MMR germline alterations are enriched among patients with UM and may contribute to oncogenesis of UM, and that UM may therefore be a rare tumor manifestation of Lynch syndrome.

Background ELP1 pathogenic variants (PV) have been recently identified as the most frequent variants predisposing to Sonic Hedgehog (SHH) medulloblastomas (MB); however, guidelines are still lacking for genetic counseling in this new syndrome.Methods We retrospectively reviewed clinical and genetic data of a French series of 29 ELP1-mutated MB.Results All patients developed SHH-MB, with a biallelic inactivation of PTCH1 found in 24 tumors. Other recurrent alterations encompassed the TP53 pathway and activation of MYCN/MYCL signaling. The median age at diagnosis was 7.3 years (range: 3-14). ELP1-mutated MB behave as sporadic cases, with similar distribution within clinical and molecular risk groups and similar outcomes (5 y - OS = 86%); no unusual side effect of treatments was noticed. Remarkably, a germline ELP1 PV was identified in all patients with available constitutional DNA (n = 26); moreover, all tested familial trio (n = 11) revealed that the PVs were inherited. Two of the 26 index cases from the French series had a family history of MB; pedigrees from these patients and from 1 additional Dutch family suggested a weak penetrance. Apart from MB, no cancer was associated with ELP1 PVs; second tumors reported in 4 patients occurred within the irradiation fields, in the usual time-lapse for expected radiotherapy-induced neoplasms.Conclusions The low penetrance, the "at risk' age window limited to childhood and the narrow tumor spectrum, question the actual benefit of genetic screening in these patients and their family. Our results suggest restricting ELP1 germline sequencing to patients with SHH-MB, depending on the parents" request.

AbstractBackgroundDespite recent advances in prenatal genetic diagnosis, medical geneticists still face considerable difficulty in interpreting the clinical outcome of copy‐number‐variant duplications and defining the mechanisms underlying the formation of certain chromosomal rearrangements.Optical genome mapping (OGM) is an emerging cytogenomic tool with proved ability to identify the full spectrum of cytogenetic aberrations.MethodsHere, we report on the use of OGM in a prenatal diagnosis setting. Detailed breakpoint mapping was used to determine the relative orientations of triplicated and duplicated segments in two unrelated foetuses harbouring chromosomal aberrations: a de novo 15q23q24.2 triplication and a paternally inherited 13q14.2 duplication that overlapped partially with the RB1 gene.ResultsOGM enabled us to suggest a plausible mechanism for the triplication and confirmed that the RB1 duplication was direct oriented and in tandem. This enabled us to predict the pathogenic consequences, refine the prognosis and adapt the follow‐up and familial screening appropriately.ConclusionAlong with an increase in diagnostic rates, OGM can rapidly highlight genotype–phenotype correlations, improve genetic counselling and significantly influence prenatal management.

Abstract BACKGROUND Medulloblastomas (MB) Sonic hedgehog (SHH) subtype are associated with a cancer predisposition syndrome (CPS) in about 15% of cases, the most frequent being related to ELP1 pathogenic variant (PV). The aim of our study is to better evaluate penetrance of this CPS and detail the characteristics of the related tumors. METHODS Twenty-nine ELP1-mutated MB identified in France were retrospectively reviewed. Molecular characteristics of the tumor and clinical features of the patients were collected; whenever possible, the germline DNA from patients and their relatives were sequenced. RESULTS All patients (sex ratio 16/13) presented with SHH-MB, mostly nodular desmoplastic (n=20/28), between 3 and 15 years of age (median 7.3). All mutations are found in the germline when a constitutional DNA sample was available (n=26). Most tumors (93%) showed a biallelic inactivation of PTCH1, other recurrent alterations concerned the TP53 pathway (including 1 somatic TP53 VP) and activation of MYCN/MYCL signaling. We observed that ELP1-mutated MB behave as sporadic cases, with similar distribution within clinical and molecular risk groups of MB, similar outcomes (5y-OS = 85%) and no unusual side effects of treatments. Three patients developed a second tumor (2 high-grade gliomas and 1 thyroid carcinoma) within the irradiation fields. All germline PV were inherited from one asymptomatic parent (11 trio). No specific morphological features were mentioned. Only two index cases from the 29 French patients had a previous familial history of MB (occurring in a cousin), with many asymptomatic carriers. Except the MB, no other cancer was significantly associated with the ELP1 PV. CONCLUSIONS the low penetrance, the ‘at risk’ age window limited to childhood and the narrow tumor spectrum, question the actual benefit of genetic screening in these patients and their family. Our results suggest restricting ELP1 germline sequencing to patients with MB, depending on the parents’ request.

Background Rhabdoid tumors (RT) are aggressive, rare tumors predominantly affecting young children, characterized by biallelic SMARCB1 gene inactivation. While most SMARCB1 alterations are acquired de novo, a third of cases exhibit germline alterations, defining Rhabdoid Tumors Predisposition Syndrome. With the increased sensitivity of next-generation sequencing (NGS), mosaicisms in genes linked to genetic diseases are more detectable. This study focuses on exploring SMARCB1 germline alterations, notably mosaicism in blood samples of children with RT and in parents, using a custom NGS panel.Methods A cohort of 280 children and 140 parents with germline analysis was studied. Germline DNA from 111 children with RT and 32 parents were reanalyzed with a custom NGS panel with 1500X average depth targeting the SMARCB1 gene to identify intragenic variants not detected with conventional low-sensitivity methods. Follow-up data was obtained for 77 patients.Results Nine previously undetected mosaicism cases were identified, totaling 17/280 patients with a mosaic variant (6.1%) in the cohort, with variant allele frequencies between 0.9% and 33%, thus highlighting the prior underestimation of its prevalence. Follow-up data showed that 4 out of 7 survivors with mosaic variants developed distinct novel tumors, 2 sharing SMARCB1 alterations with the initial tumor, emphasizing the potential clinical impact of SMARCB1 mosaicism.Conclusions The hitherto underestimated rate of SMARCB1 mosaicism in RT underscores the need for optimized genetic counseling and oncological monitoring. The findings have significant medical implications, considering the dire prognosis of RT. Graphical Abstract

About half of the human genome is composed of repeated sequences derived from mobile elements, mainly retrotransposons, generally without pathogenic effect. Familial forms of retinoblastoma are caused by germline pathogenic variants in RB1 gene. Here, we describe a family with retinoblastoma affecting a father and his son. No pathogenic variant was identified after DNA analysis of RB1 gene coding sequence and exon-intron junctions. However, RB1 mRNA analysis showed a chimeric transcript with insertion of 114 nucleotides from HPF1 gene inside RB1 gene. This chimeric transcript led to an insertion of 38 amino acids in functional domain of retinoblastoma protein. Subsequent DNA analysis in RB1 intron 17 revealed the presence of a full-length HPF1 retrogene insertion in opposite orientation. Functional assay shows that this insertion has a deleterious impact on retinoblastoma protein function. This is the first report of a full-length retrogene insertion involved in human Mendelian disease leading to a chimeric transcript and a non-functional chimeric protein. Some retrogene insertions may be missed by standard diagnostic genetic testing, so contribution of retrogene insertions to human disease may be underestimated. The increasing use of whole genome sequencing in diagnostic settings will help to get a more comprehensive view of retrogenes.