Abstract IA029: The origins of leiomyosarcoma: implications for prognosis and defining new therapeutic options

Abstract

Abstract Introduction: Leiomyosarcomas (LMS) are genetically heterogenous tumors differentiating along smooth muscle lines. Currently, LMS treatment is not informed by molecular subtyping and is associated with highly variable survival. While disease site continues to dictate clinical management, the contribution of genetic factors to LMS subtype, origins, and timing are unknown. Here we analyze 70 genomes and 130 transcriptomes of LMS, including multiple tumor regions and paired metastases, with the goal of defining the molecular origins of LMS and using both computational analysis and functional genomics to define new therapeutic arenas for metastatic disease. Results: Molecular profiling highlight the very early origins of LMS. We uncover three specific subtypes of LMS that likely develop from distinct lineages of smooth muscle cells. Of these, dedifferentiated LMS with high immune infiltration and tumors primarily of gynecological origin harbor genomic dystrophin deletions and/or loss of dystrophin expression, acquire the highest burden of genomic mutation, and are associated with worse survival. Homologous recombination defects lead to genome-wide mutational signatures, and a corresponding sensitivity to PARP trappers and other DNA damage response inhibitors, suggesting a promising therapeutic strategy for LMS. Finally, by phylogenetic reconstruction, we present evidence that clones seeding lethal metastases arise decades prior to LMS diagnosis. Conclusions: In summary, LMS, the catch all-label for any primary malignant smooth muscle neoplasm, encompasses at least three distinct entities. We report that the utility of DNA damage response inhibitors is promising and warrants further exploration. Finally, the molecular evolution and timing of LMS provide a broad window for early intervention and risk stratification for these patients. Citation Format: Rebecca A. Gladdy. The origins of leiomyosarcoma: implications for prognosis and defining new therapeutic options [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr IA029.