Genomic insights and therapeutic efficacy of PARP inhibitors in a high-LOH patient-derived xenograft from malignant transformation of ovarian teratoma.

The malignant transformation of ovarian mature cystic teratoma (MTMCT) is a rare and aggressive condition often diagnosed at advanced stages with limited treatment options. Leveraging cancer genomic profiling (CGP), this study evaluated the efficacy of poly(ADP-ribose) polymerase (PARP) inhibitors in a patient-derived xenograft (PDX) model of MTMCT with high loss of heterozygosity (LOH). Tumor samples from a patient with MTMCT were used to establish the PDX model. CGP revealed high LOH and actionable mutations, including STK11 (E256*) and EMSY amplification, suggesting potential sensitivity to PARP inhibitors. Mice treated with PARP inhibitors exhibited significantly reduced tumor volumes compared to controls. Whole-exome sequencing (WES) performed on control and post-treatment residual tumors demonstrated that while total LOH levels remained stable, copy-neutral LOH (CN-LOH) increased significantly, indicating treatment-induced genomic instability. Notably, STK11 (E256*) underwent CN-LOH in residual tumors, suggesting a role in acquired resistance. Furthermore, EMSY amplification, initially observed in the tumor and associated with PARP inhibitor sensitivity, was absent after treatment, reflecting clonal selection or adaptive resistance. These findings underscore the therapeutic potential of PARP inhibitors in high-LOH MTMCT while highlighting the emergence of resistance mechanisms, including CN-LOH and loss of EMSY amplification. They emphasize the importance of considering tumor evolution and treatment timing when interpreting CGP results, providing a foundation for further research into predictive biomarkers and resistance mechanisms in rare gynecologic malignancies.