Schultz, Kris Ann P.

Abstract INTRODUCTION: Pleuropulmonary blastoma (PPB) and Sertoli-Leydig cell tumor (SLCT) are DICER1-related tumors for which novel therapies are urgently needed. A subset of Wilms tumors are also associated with germline or somatic variants in DICER1. Current therapies include cytotoxic chemotherapy, radiation, and surgery, but there are limited options for patients with recurrent disease. Antibody-Drug Conjugates (ADC) have emerged as promising therapies for several solid tumors. Aberrantly expressed cell surface proteins, including Preferentially Expressed Antigen in Melanoma (PRAME), represent potential targets for immunotherapeutic treatments like CAR-T cell and antibody-based therapies in malignant cancers, including DICER1-associated tumors. METHODS: Individuals diagnosed with PPB, SLCT, and Wilms tumor who enrolled in the International PPB/DICER1 Registry, International OTST Registry, and/or UT Southwestern Pediatric Hematology-Oncology Biorepository were selected for analysis. We analyzed ten PPB samples (four PDX, six primary tumor), four SLCT samples (all primary tumor), and 54 Wilms tumor samples (4 PDX, 50 primary tumor). DICER1 hotspot variants were verified in all 14 PPB and SLCT samples, while none of the Wilms tumor samples we analyzed exhibited DICER1 hotspot variants. Mapped and normalized whole-transcriptome sequencing reads were used to examine expression of 73 targets of antibody- or cell-based therapies that are clinically approved or under clinical investigation on clinicaltrials.gov. Genes with a median expression exceeding 2.5 transcripts per million (TPM) were considered expressed in a given tumor type; this threshold was selected to be permissive in identifying potential targets for further evaluation. RESULTS: Of the 73 genes of interest, 21 targetable cell-surface genes met a median expression threshold of 2.5 TPM in at least one tumor type: 11 genes in PPB, 16 in SLCT, and 14 in Wilms. Seven genes (FN1, PRAME, MCAM, CD248, IL11RA, CD276 (B7-H3), and MRC2) were expressed at this level in all three tumor types. Additional genes were expressed above this level in only two of the tumor types; PDGFRA in PPB and SLCT; GPC2 and TYRO3 in SLCT and Wilms tumor; and CSPG4, ERBB2, FZD10 in PPB and Wilms tumor. Six genes were exclusively expressed in SLCT (AXL, GPNMB, PROM1, KDR, ITGA6, FGFR4), and two were unique to Wilms tumor (GPC1, ULBP3). Of these, PRAME was previously reported as frequently expressed in DICER1-associated tumors; little has been reported about the remaining potential targets. CONCLUSION: PPB, SLCT, and Wilms tumor express several potential immunotherapy targets by RNA-seq. Expression of these potential targets should be investigated by immunostaining in a wider panel of tumors. Further study on the potential for ADCs or CAR-T cell therapies to treat DICER1-related conditions is needed. Citation Format: Brenya McNally, BS, Paige H.R. Mallinger, MS, David Huntsman, MD, FRCPC, FCCMG, Yemin Wang, PhD, Joyce Zhang, PhD, Claudette R. Fraire, PhD, Peter J. Schoettler, MD, Kris Ann P. Schultz, MD, Kenneth S. Chen, MD. Identifying potential cell-surface targets for therapeutic treatment of DICER1-related cancers [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Breaking Barriers in the Fight against Rare Cancers; 2026 Jul 18-20; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2026;86(14_Suppl):Abstract nr A018.

PURPOSE Sertoli-Leydig cell tumors (SLCTs) are rare sex cord-stromal tumors, representing <0.5% of all ovarian tumors. We analyze the role of germline DICER1 status in outcomes of ovarian SLCT. METHODS Patients with SLCT were enrolled in the International Pleuropulmonary Blastoma/ DICER1 Registry and/or the International Ovarian and Testicular Stromal Tumor Registry. Medical records were systematically abstracted, and those with known germline DICER1 status were selected for analysis. RESULTS Of 162 patients with SLCT, 60% had a germline DICER1 pathogenic or likely pathogenic (P/LP) variant. The adjusted 3-year recurrence-free survival (RFS) was 87.2% (95% CI, 79.4 to 95.8) for patients with a germline DICER1 P/LP variant compared with 78.1% (95% CI, 66.4 to 91.9) for those without a germline DICER1 P/LP variant ( P = .043). The adjusted 3-year and 5-year overall survival (OS) was 93.9% (95% CI, 87.3 to 100.0) for those with a germline DICER1 P/LP variant compared with the 3-year OS of 91.3% (95% CI, 83.4 to 100.0) and the 5-year OS of 78.2% (95% CI, 63.8 to 95.9) for those without a germline DICER1 P/LP variant ( P = .021). Among patients with a germline DICER1 P/LP variant, the risk of a subsequent, nonrecurrent event was 36.2% (95% CI, 21.4 to 48.1) within 10 years. Previous/concurrent and subsequent neoplasms were rare among those without a germline DICER1 P/LP variant. CONCLUSION This cohort study of patients with SLCT demonstrated that those with germline DICER1 P/LP variants had superior RFS and OS even when adjusting for other prognostic factors. Beyond prognostic implications of a germline DICER1 P/LP variant, germline testing helps identify patients at risk of subsequent neoplasms, including metachronous SLCT.

AbstractBackgroundOvarian juvenile granulosa cell tumors (juvGCT) are rare sex cord‐stromal tumors that occur primarily in children and adolescents. This study summarizes the clinical presentation and outcomes of patients with juvGCT.MethodsPatients were enrolled in the International Ovarian and Testicular Stromal Tumor and/or International Pleuropulmonary Blastoma/DICER1 Registries. Available medical records were abstracted, and pathology was centrally reviewed. Surgical staging was classified using the 2014 International Federation of Gynecology and Obstetrics (FIGO) criteria.ResultsIn total, 70 patients with juvGCT enrolled and were diagnosed between 2001 and 2024; most patients (81%, 57 of 70) presented with FIGO stage I disease. Adjuvant chemotherapy was given in 30% (21 of 70); all regimens were platinum‐based. Three‐year event‐free survival among patients with stage IA tumors was 80.2% (95% confidence interval [CI], 62.4%–100.0%), IC1 was 87.4 (95% CI, 72.4%–100.0%), IC2‐IC3 was 63.6% (95% CI, 40.7%–99.5%), and II‐IV was 48% (95% CI, 24.6%–93.8%). Of the patients with recurrent juvGCT with known mitotic index (MI), all had MI greater than 19 mitoses per 10 high power fields (HPF) at diagnosis.ConclusionOutcomes were worse for patients with FIGO stage ≥IC2 disease and for tumors with >19 mitoses per 10 HPF. Given the prognostic significance of MI, the authors strongly recommend the assessment of MI for all juvGCTs. More information about tumor biology is critical to identify which patients may benefit from adjuvant chemotherapy and to facilitate the development of novel therapies.

Abstract Purpose: DROSHA, DGCR8, and DICER1 regulate miRNA biogenesis and are commonly mutated in cancer. Although DGCR8 and DICER1 germline pathogenic variants (GPV) cause autosomal dominant tumor predisposition, no association between DROSHA GPVs and clinical phenotypes has been reported. Experimental Design: After obtaining informed consent, sequencing was performed on germline and tumor samples from all patients. The occurrence of germline DROSHA GPVs was investigated in large pediatric and adult cancer datasets. The population prevalence of DROSHA GPVs was investigated in the UK Biobank and Geisinger DiscovEHR cohorts. Results: We describe nine children from eight families with heterozygous DROSHA GPVs and a diagnosis of pineoblastoma (n = 8) or Wilms tumor (n = 1). A somatic second hit in DROSHA was detected in all eight tumors analyzed. All pineoblastoma tumors analyzed were classified as miRNA processing–altered 1 subtype. We estimate the population prevalence of germline DROSHA loss-of-function variants to be 1:3,875 to 1:4,843 but find no evidence for increased adult cancer risk. Conclusions: This is the first report of DROSHA-related tumor predisposition. As pineoblastoma and Wilms tumor are also associated with DICER1 GPVs, our results suggest that the tissues of origin for these tumors are uniquely tolerant of general miRNA loss. The miRNA processing–altered 1 pineoblastoma subtype is associated with older age of diagnosis and better outcomes than other subtypes, suggesting DROSHA GPV status may have important clinical and prognostic significance. We suggest that genetic testing for DROSHA GPVs be considered for patients with pineoblastoma, Wilms tumor, or other DICER1-/DGCR8-related conditions and propose surveillance recommendations through research studies for individuals with DROSHA GPVs.

Abstract Purpose: DICER1-related tumor predisposition increases risk for a spectrum of benign and malignant tumors. In 2018, the International Pleuropulmonary Blastoma (PPB)/DICER1 Registry published guidelines for testing- and imaging-based surveillance of individuals with a known or suspected germline DICER1 pathogenic or likely pathogenic (P/LP) variant. One of the goals of the Registry is to continue to refine these guidelines as additional data become available. Experimental Design: Individuals were enrolled in the International PPB/DICER1 Registry, the International Ovarian and Testicular Stromal Tumor Registry, and/or the NCI Natural History of DICER1 Syndrome study. Results: Review of participant records identified 713 participants with a germline DICER1 P/LP variant from 38 countries. To date, 5 cases of type I and 29 cases of type Ir PPB have been diagnosed by surveillance in enrolled individuals. One hundred and three individuals with a germline P/LP variant developed a primary ovarian Sertoli–Leydig cell tumor at a median age of 14 years (range: 11 months–66 years); 13% were diagnosed before 8 years of age, the current age of onset of pelvic surveillance. Additionally, 4% of Sertoli–Leydig cell tumors were diagnosed before 4 years of age. Conclusions: Ongoing data collection highlights the role of lung surveillance in the early detection of PPB and suggests that imaging-based detection and early resection may decrease the risk of advanced PPB. DICER1-related ovarian tumors were detected before 8 years of age, prompting the Registry to recommend earlier initiation of ovarian surveillance with pelvic ultrasound beginning at the time of detection of a germline DICER1 P/LP variant.

Abstract Background Anaplastic sarcoma of the kidney (ASK) is a DICER1 ‐related neoplasm first identified as a distinctive tumor type through the evaluation of unusual cases of putative anaplastic Wilms tumors. Subsequent case reports identified the presence of biallelic DICER1 variants as well as progression from cystic nephroma, a benign DICER1 ‐related neoplasm. Despite increasing recognition of ASK as a distinct entity, the optimal treatment remains unclear. Methods Individuals with known or suspected DICER1 ‐related tumors including ASK were enrolled in the International Pleuropulmonary Blastoma/ DICER1 Registry. Additionally, a comprehensive review of reported cases of ASK was undertaken, and data were aggregated for analysis with the aim to identify prognostic factors and clinical characteristics to guide decisions regarding genetic testing, treatment, and surveillance. Results Ten cases of ASK were identified in the Registry along with 37 previously published cases. Staging data, per Children's Oncology Group guidelines, was available for 40 patients: 13 were stage I, 12 were stage II, 10 were stage III, and five were stage IV. Outcome data were available for 37 patients. Most (38 of 46) patients received upfront chemotherapy and 14 patients received upfront radiation. Two‐year event‐free survival (EFS) for stage I–II ASK was 81.8% (95% confidence interval [CI]: 67.2%–99.6%), compared with 46.6% EFS (95% CI: 24.7%–87.8%) for stage III–IV ( p = .07). Two‐year overall survival (OS) for stage I–II ASK was 88.9% (95% CI: 75.5%–100.0%), compared with 70.0% (95% CI: 46.7%–100.0%) for stage III–IV ( p = .20). Chemotherapy was associated with improved EFS and OS with hazard ratios of 0.09 (95% CI: 0.02–0.31) and 0.08 (95% CI: 0.02–0.42), respectively. Conclusion ASK is a rare DICER1 ‐related renal neoplasm. In the current report, we identify clinical and treatment‐related factors associated with outcome including the importance of chemotherapy in treating ASK. Ongoing data collection and genomic analysis are indicated to optimize outcomes for children and adults with these rare tumors.

10538 Background: Rhabdomyosarcoma (RMS) of the female genital tract is rare, accounting for 3.5% of cases of rhabdomyosarcomas. Germline DICER1 mutations are associated with predisposition to pleuropulmonary blastoma and other tumors including sarcomas. Recently DICER1-associated RMS of the uterus/ovary has ben reported.. The aim of this study is to evaluate demographic characteristics, molecular pathogenesis, treatment and long term outcome of female genital tract rhabdomyosarcoma. Methods: Files of children with RMS of the female genital tract diagnosed at the Istanbul University, Oncology Institute during 1990-2019 were reviewed. Molecular genetic sequencing was performed by polymerase chain reaction amplification of genomic DNA extracted from the formalin-fixed, paraffin embedded tumors, followed by Sanger sequencing. Genetic testing for DICER1 variants of the proband and family members was performed if DICER1 mutation was detected in the tumor of the proband. Results: Of 210 RMS cases, 11 arose from the female genital tract. The median age at diagnosis was 52 months (10 months-15 years). Primary sites were vaginal (n = 5), uterus (n = 4), and ovary(n = 2). Presenting symptoms included vaginal mass (n = 6), vaginal bleeding (n = 5), and abdominal pain (n = 3). Four had group 1, five group 3, two group 2 disease and all received chemotherapy (vincristine, actinomycinD + cyclophosphamide).Three received radiotherapy; three underwent hysterectomy. DICER1 mutation was detected in tumor tissue in three patients:[ c.5113G > A (p.E1705K); c.5428G > T (p.D1810Y); c.1870C > T (p.Arg624Ter)] Genetic testing revealed germline DICER1 pathogenic variation in two patients and their family members, one of whom had cystic nephroma in infancy and history of Wilms tumor in an uncle. They were referred for surveillance for the DICER1 related diseases. A patient with metachronous bilateral ovarian RMS died. Two are married, one has children. The 5 year survival for RMS of the female genital tract was 85.7 % at a median follow-up of 34 (4-298) months. Conclusions: Rhabdomyosarcoma of the female genital tract is associated with a favorable prognosis, however some individuals undergo aggressive local therapies. Individuals with RMS of the female genital tract should be tested for DICER1 pathogenic variation. The detection of a DICER1 mutation in an individual or family members is important to facilitate surveillance for related tumors, so that they may be detected at the earliest possible stage, potentially increasing survival and decreasing risks of late effects.