Abstract A012: THROUGH THE LENS OF TUMOR HETEROGENEITY: UNRAVELING DEVELOPMENTAL DYNAMICS AND CHEMOTHERAPY RESISTANCE IN RETINOBLASTOMA

Retinoblastoma is a rare and aggressive pediatric tumor of the developing retina that originates in utero following biallelic inactivation of the tumor suppressor gene RB1. The early onset and biological complexity of this disease present unique challenges for researchers and clinicians, including difficulties in diagnosis and variability in treatment outcomes. Tumor heterogeneity in retinoblastoma arises from cellular, genetic, and developmental differences. Patients with germline RB1 mutations, and to a lesser extent those without, often develop multifocal tumors, though the origins and relationships between these lesions have remained unclear. Histopathological studies suggest that retinoblastoma tumors consist of two major cellular populations resembling either photoreceptors or retinal progenitor cells. However, molecular characterization of retinoblastoma tumors has historically been limited to cases of advanced disease requiring enucleation of the eye, restricting opportunities for comprehensive research on earlier stages of tumor development. To address this challenge, retinal organoids differentiated from stem cells were used to model early developmental stages of the retina and to study tumor initiation in a controlled environment. Patient-derived xenograft models were employed to investigate tumor progression, heterogeneity, and response to treatment in advanced disease. Additionally, single-cell RNA sequencing and cellular barcoding enabled detailed analysis of the developmental trajectory and differentiation status of tumor cell populations, revealing their roles in disease initiation, progression, and therapeutic outcomes. Our study definitively demonstrates the relationship between two the major cellular populations in retinoblastoma tumors: photoreceptor-like and progenitor-like cells. We further reveal that chemotherapy preferentially targets one of these populations, challenging traditional assumptions about treatment mechanisms and highlighting the influence of development and differentiation status on therapeutic outcomes. These findings underscore the critical importance of developmental heterogeneity in retinoblastoma biology and its influence on treatment response. By redefining the interplay between tumor composition and therapeutic outcomes, our work provides a foundation for developing more precise and effective treatment strategies for this devastating childhood cancer. Citation Format: Shannon R Sweeney, Madison Parks, Jackie Norrie, Asha Jacob Jannu, Cody Ramirez, Michael A Dyer. THROUGH THE LENS OF TUMOR HETEROGENEITY: UNRAVELING DEVELOPMENTAL DYNAMICS AND CHEMOTHERAPY RESISTANCE IN RETINOBLASTOMA [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 A012.