Nguyen, Timmy

3601 Background: Two cfDNA assays are FDA-approved for use in advanced cancer pts across solid tumors. While several NCCN guidelines recommend cfDNA as a valid and useful method for molecular testing, the utility varies by cancer type. Despite the growing number of molecular alterations pertinent to first-line treatment in mCRC, current guidelines offer little guidance on the use of cfDNA in mCRC. Here we assess the ability of cfDNA to detect guideline-relevant actionable biomarkers informative for first-line therapy selection and beyond in patients with mCRC. Methods: We queried consecutive samples from advanced cancer pts with a diagnosis of CRC who underwent testing via a commercially available cfDNA assay (Guardant360) from September 2018 to January 2022. Validation and content of this assay has been previously described. To enrich for less heavily treated pts, we limited analysis to those whose first cfDNA test was done during the study period and only included the pt’s first test. The maximum variant allele fraction (maxVAF) for each test was used as a proxy for tumor shed and was compared between cancers with a Mann-Whitney test. The frequency of suspected germline alterations was assessed only in pts who received testing via a panel version with expanded mismatch repair (MMR) gene coverage. Tissue frequencies for select biomarkers were obtained from the MSK-IMPACT Clinical Sequencing Cohort in cBioPortal. Results: In total, 14,345 pts with mCRC received their first cfDNA test during the study period, with 92% of pts (13,190) having >1 cfDNA alteration detected. Median age was 62 and 44% of pts were female. The frequencies of key biomarkers are listed in Table 1. The median maxVAF was 5.6%, compared to 2.5% and 1.8% for pts with advanced gastric and NSCLC, respectively (p = < 0.0001 for both). The average turnaround time (TAT) for tests was 7 calendar days. Conclusions: cfDNA results from pts with mCRC demonstrated detection of biomarkers essential to first-line treatment decisions at a frequency comparable to what has been reported via tissue genotyping. mCRC pts had significantly higher tumor shed compared to other cancer types with guidelines that recommend cfDNA as an option for molecular testing, suggesting a potential gap in coverage. Tissue availability in mCRC does not guarantee comprehensive testing is completed quickly (compared to the 7-day TAT seen for cfDNA here), making it an attractive alternative strategy for first-line therapy selection in mCRC. [Table: see text]

AbstractPurpose:To analytically and clinically validate microsatellite instability (MSI) detection using cell-free DNA (cfDNA) sequencing.Experimental Design:Pan-cancer MSI detection using Guardant360 was analytically validated according to established guidelines and clinically validated using 1,145 cfDNA samples for which tissue MSI status based on standard-of-care tissue testing was available. The landscape of cfDNA-based MSI across solid tumor types was investigated in a cohort of 28,459 clinical plasma samples. Clinical outcomes for 16 patients with cfDNA MSI-H gastric cancer treated with immunotherapy were evaluated.Results:cfDNA MSI evaluation was shown to have high specificity, precision, and sensitivity, with a limit of detection of 0.1% tumor content. In evaluable patients, cfDNA testing accurately detected 87% (71/82) of tissue MSI-H and 99.5% of tissue microsatellite stable (863/867) for an overall accuracy of 98.4% (934/949) and a positive predictive value of 95% (71/75). Concordance of cfDNA MSI with tissue PCR and next-generation sequencing was significantly higher than IHC. Prevalence of cfDNA MSI for major cancer types was consistent with those reported for tissue. Finally, robust clinical activity of immunotherapy treatment was seen in patients with advanced gastric cancer positive for MSI by cfDNA, with 63% (10/16) of patients achieving complete or partial remission with sustained clinical benefit.Conclusions:cfDNA-based MSI detection using Guardant360 is highly concordant with tissue-based testing, enabling highly accurate detection of MSI status concurrent with comprehensive genomic profiling and expanding access to immunotherapy for patients with advanced cancer for whom current testing practices are inadequate.See related commentary by Wang and Ajani, p. 6887

284 Background: ODSH, a low anticoagulant heparin derivative, interferes with several important pancreatic cancer cell survival pathways. A randomized phase II trial was initiated to determine if ODSH improves the activity of G/A, a promising pancreatic cancer investigational therapy. Preliminary data are presented here for the first 10 patients administered ODSH as part of an initial run-in phase prior to patient randomization. Methods: Patients with previously untreated, metastatic pancreatic cancer were treated with G (1,000 mg/m2) and A (125 mg/m2) plus ODSH (4 mg/kg bolus followed by a 48 hr. continuous IV infusion at a dose of 0.375 mg/kg/hr) on days 1, 8, and 15 every 28 days until disease progression or unacceptable toxicity. Patients were required to have ECOG ≤ 1 and appropriate blood and liver function levels. The primary endpoint was progression-free survival (PFS). Results: 10 patients (median age, 66 years) were administered up to 5 cycles of G/A plus ODSH. Per RECIST criteria, a partial response (PR) was achieved in 5 patients (50%) and the median PFS will exceed 6 months. Disease control (PR or stable disease for > 16 weeks) occurred in all 10 patients. Of 9 patients with baseline elevated CA 19-9 levels, 8 had > 60% reduction. ODSH was well tolerated and unexpectedly appeared to preserve marrow function as no patients had grade 3/4 thrombocytopenia or grade 4 neutropenia during any of the cycles. Conclusions: Although G/A and FOLFIRINOX are important advances, additional progress is necessary for metastatic pancreatic cancer patients. ODSH may interfere with pancreatic cancer invasion, metastasis, and chemo-resistance by inhibiting P- and L-selectins, heparanase, and the HMGB1-RAGE axis, respectively, suggesting that ODSH may enhance chemotherapy activity. This preliminary analysis in a small number of patients is encouraging and consistent with a previous report for this regimen (Von Hoff, J Clin Oncol, 2011). ODSH has also been very well tolerated and early data suggests that it may preserve platelet and neutrophil levels. Further follow-up of the ongoing randomized phase II trial is warranted. Clinical trial information: NCT01461915.