Citations

4157 Background: IDH1/2 mutations occur in ~25% of cholangiocarcinomas (CCAs). Preclinical studies suggest synergy between PARP inhibition and PD-L1 blockade. We previously conducted a phase II trial of olaparib plus durvalumab in advanced IDH -mutant CCA. We report matched baseline tissue and serial cell-free DNA (cfDNA)-based correlative analysis of pts samples. The primary objective was to develop a cfDNA methylome signature as a non-invasive biomarker. Methods: This single-arm, open-label phase II study (NCT03991832) enrolled patients with unresectable/metastatic IDH -mutant CCA and ≤2 prior lines of systemic therapy. Patients received olaparib 300 mg orally twice daily and durvalumab 1500 mg IV every 4 weeks. Blood samples were collected at baseline and monthly while on treatment for planned correlatives to examine R2HG, S2HG, and artemin levels using HPLC (High-Performance Liquid Chromatography). Cell-free methylated DNA immunoprecipitation and high-throughput sequencing (cfMeDIP-seq) was performed on pts cfDNA samples and case-matched IDH -wildtype pts. Formalin-fixed, paraffin-embedded blocks of baseline tumor biopsies were used for multispectral fluorescent IHC (FL-IHC) using a 6-marker panel composed of pan-cytokeratin, CD4, CD8, CD163, PD-L1, and CD68. Results: Ten patients were enrolled (median age 63.5 y; 50% female; 90% received prior platinum). Median treatment duration was 1.95 mo (range 1.8–13.5). No complete or partial responses were observed. DCR was 30% (3 patients with stable disease); one patient remained on therapy for 13.5 mo before progression. Median PFS was 1.97 mo (95% CI 1.73–3.93). HPLC from baseline plasma showed lower baseline artemin levels correlated with stable disease (p=0.038), while R2HG/S2HG ratios showed no association with outcome. FL-IHC showed enriched immune cell populations, specifically CD4 + T cells (p=0.0032) and a trend for CD68 + macrophages (p=0.062), in the tumor stroma compared with tumor core. 54 plasma samples (from 8 patients) were profiled with cfMeDIP-seq along with 8 IDH -wildtype controls. Using top 100 differentially methylated regions, the circulating tumour DNA methylome exhibited a highly specific signature, accurately discriminating IDH -mutant and IDH -wildtype CCA regardless of treatment status. The specific differentially methylated gene pathways between groups were comprehensively examined in both on-treatment and baseline plasma samples. Conclusions: Advanced IDH -mutant CCA harbors an immune-excluded phenotype, which may underlie primary resistance to immunotherapy. Plasma cfDNA methylome signature can accurately discriminate CCA with IDH mutations. Clinical trial information: NCT03991832 .

TPS4205 Background: Multiple lines of evidence support the use of platinum-based chemotherapy for patients with homologous recombination deficiency-associated pancreatic adenocarcinoma (HRD PDAC; 15-20%). However, the impact of the specific platinum agent used remains uncertain. Mechanistically, oxaliplatin and cisplatin act distinctly on cancer cells, reflected in disparate toxicity profiles and target disease indications; furthermore, preclinical studies have shown that BRCA2-deficient cell lines and mice demonstrate significantly greater sensitivity to cisplatin compared to oxaliplatin. While oxaliplatin, part of the FOLFIRINOX regimen, represents the most commonly used platinum analogue for PDAC, clinical data shows that cisplatin (in combination with gemcitabine) can produce robust response rates (~70%) specifically in patients with germline BRCA/PALB2-mutated metastatic PDAC. We therefore designed a randomized clinical trial (PLATINUM) through the Alliance for Clinical Trials in Oncology cooperative group to assess the optimal chemotherapy regimen in patients with HRD-associated metastatic PDAC following front-line FOLFIRINOX and to test the hypothesis that a platinum switch strategy will be beneficial. Methods: The study consists of a seamless phase II/III design, with the primary endpoint of the phase III component being overall survival. Eligible patients will have metastatic PDAC, a confirmed pathogenic BRCA1/2 or PALB2 mutation (somatic or germline), and demonstrated disease progression on front-line FOLFIRINOX, with or without subsequent PARP inhibitor maintenance. Patients will be randomized 1:1 to receive (1) the de facto standard of gemcitabine plus nab-paclitaxel; or (2) the experimental 3-drug combination of gemcitabine, nab-paclitaxel, and cisplatin (NABPLAGEM), which has been previously studied in non-biomarker-selected patients with advanced biliary tract cancer (SWOG1815) and metastatic PDAC. Both treatment arms will use a once every other week dosing schedule. A total of 100 patients will be enrolled, which provides 90% power to detect an effect size of hazard ratio 0.5 (median OS of 18 vs 9 months) at a one-sided alpha of 0.05. Reports containing efficacy, adverse events, and administrative information will be provided to the Alliance DSMB every 6 months. Planned correlatives include ctDNA analysis for BRCA reversion mutations in all patients, as well as whole genome and transcriptome sequencing in an optional biopsy cohort. This study was activated in December 2023. Clinical trial information: NCT06115499 .