Introduction: KRASG12D is the most common KRAS mutation in pancreatic ductal adenocarcinoma (PDAC). It is well known that activating point mutations in one allele are sufficient for tumor growth in patients harboring KRASG12D mutations and it is challenging to target this mutation with effective KRASG12D inhibitors. Driver gene amplification is a known mechanism of acquired resistance to therapy in pancreatic cancers. Although other genetic features, such as KRAS gene copy number variations (CNV) and mutant allele fractions (MAF), have been observed, their influence on response to treatment remains unclear. Current discovery revealed that MRTX1133 is a potent, non-covalent and high-affinity small molecule that selectively targets KRASG12D. Therefore, with the efforts underway to develop effective therapy response using the KRASG12D-targeted drug, MRTX1133, it is paramount to improve our understanding regarding the role of KRAS CNV/MAF in PDAC. Methods: Using quantitative digital PCR (DPCR), we first measured the absolute copy number of KRAS wild type (WT), and mutant type (MT) and we then calculated MAF by formula: MAF = MT allele numbers/(MT+WT allele numbers) in DNA from various KRASG12D mutant PDAC cell lines and PDX-derived primary cell lines. 3D viability and cell signaling assays determined sensitivity to MRTX1133 in established and PDX-derived primary cell lines in vitro. We also assessed the representative KRAS gene CNV of those cell lines by TaqMan real time PCR. DPCR was also utilized to determine the MAF in PDX-derived tissues. Results: We found a trend in response to MRTX1133 in KRASG12D cell lines based on their MAF and representative KRAS gene CNV. Resistant, and sensitive KRASG12D cell lines have average MAF of 75.23%, and 52.81% respectively. Most of the resistant cells have higher KRAS gene copy number gain (6-8) compared to sensitive cells (3-4). Interestingly, our data suggests that higher MAF (>53%) and gene copy numbers (>4) may predict a resistant phenotype in KRASG12D cells to MRTX1133. Mechanistically, MRTX1133 inhibits ERK1/2 signaling and increases apoptosis in sensitive cells. Representative sensitive and resistant cell lines are further evaluated for any changes in baseline and MRTX1133-induced MAF and copy number alterations by DPCR and TaqMan real time PCR. However, the results indicated that there are no significant differences in MAF and KRAS CNV in the sensitive and resistant cells on pre and post treatment of MRTX1133. We further extended our study by evaluating the MAF targeting KRASG12D in various PDX-derived tissues by quantitative DPCR. With exception to a few cases, most of the analyzed PDX tissues contained balanced MAF (~50%), which may show sensitivity to MRTX1133 according to our findings. Conclusions: Our current observations indicate 1) KRAS CN gain and MAF increase may appear to play major roles in the progression of a resistant phenotype 2) KRAS CNV and MAF status may contribute to criteria to select PDAC patients who are most likely to benefit from therapy with MRTX1133. Citation Format: Bhaswati Sarcar, Alexandra Tassielli, Liang Wang, Ruifan Dai, Meagan D. Read, Francisca Beato, Dae W. Kim, Pamela J. Hodul, Jennifer B. Permuth, Eric B. Haura, Mokenge P. Malafa, Jason B. Fleming. KRAS copy number variation and mutant allele fractions predict in vitro response of PDX-derived human pancreatic cancer cell lines to KRASG12D inhibitor MRTX1133 [abstract]. In: Proceedings of the AACR Special Conference: Targeting RAS; 2023 Mar 5-8; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Res 2023;21(5_Suppl):Abstract nr B032.

Introduction Metastatic pancreatic ductal adenocarcinoma (PDAC) carries a poor prognosis and significant morbidity from local tumor progression. We investigated outcomes among oligometastatic PDAC patients treated with stereotactic magnetic resonance image-guided ablative radiotherapy (SMART) to primary disease. Methods We performed a retrospective multi-institutional analysis of oligometastatic PDAC at diagnosis or with metachronous oligoprogression during induction chemotherapy treated with primary tumor SMART. Outcomes of interest included overall survival (OS), progression-free survival (PFS), freedom from locoregional failure (FFLRF), and freedom from distant failure (FFDF). Acute and late toxicity were reported and in exploratory analyses patients were stratified by the number of metastases, SMART indication, and addition of metastasis-directed therapy. Results From 2019 to 2021, 22 patients with oligometastatic PDAC (range: 1–6 metastases) received SMART to the primary tumor with a median follow-up of 11.2 months from SMART. Nineteen patients had de novo synchronous metastatic disease and three had metachronous oligoprogression. Metastasis location most commonly was liver only (40.9%), multiple organs (27.3%), lungs only (13.6%), or abdominal/pelvic nodes (13.6%). All patients received either FOLFIRINOX (64%) or gemcitabine/nab-paclitaxel (36%) followed by SMART (median 50 Gy, 5 fractions) for local control (77%), pain control (14%), or local progression (9%). Additionally, 41% of patients received other metastasis-directed treatments. The median OS from diagnosis and SMART was 23.9 months and 11.6 months, respectively. Calculated from SMART, the median PFS was 2.4 months with 91% of patients having distant progression, and 1-year local control was 68. Two patients (9%) experienced grade 3 toxicities, gastric outlet obstruction, and gastrointestinal bleed without grade 4 or 5 toxicity. Conclusion There was minimal morbidity of local disease progression after SMART in this cohort of oligometastatic PDAC. As systemic therapy options improve, additional strategies to identify patients who may derive benefits from local consolidation or metastasis-directed therapy are needed.

Background: The influence of chemotherapy type and vascular margin status after sequential chemotherapy and stereotactic body radiation therapy (SBRT) for borderline resectable pancreatic cancer (BRPC) is unknown.Methods: A retrospective review was performed on BRPC patients treated with chemotherapy and 5-fraction SBRT from 2009 to 2021. Surgical outcomes and SBRT-related toxicity were reported. Clinical outcomes were estimated by Kaplan-Meier with log rank comparisons.Results: A total of 303 patients received neoadjuvant chemotherapy and SBRT to a median dose of 40 Gy prescribed to the tumor-vessel interface and median dose of 32.4 Gyto 95% of the gross tumor volume. One hundred and sixty-nine patients (56%) were resected and benefited from improved median OS (41.1 vs 15.5 months, P < 0.001). Close/positive vascular margins were not associated with worse OS or FFLRF. Type of neoadjuvant chemotherapy did not influence OS for resected patients, but FOLFIR-INOX was associated with improved median OS in unresected patients (18.2 vs 13.1 months, P = 0.001).Conclusion: For BRPC, the effect of a positive or close vascular margin may be mitigated by neoad-juvant therapy. Shorter duration neoadjuvant chemotherapy as well as the optimal biological effective dose of radiotherapy should be prospectively explored.

Purpose: Preoperative radiation therapy (RT) for pancreatic adenocarcinoma reduces positive surgical margin rates, and when delivered to an ablative dose range it may improve local control and overall survival for patients with unresectable disease. Use of stereotactic body RT to achieve a higher biologically effective dose has been limited by toxicity to adjacent radiosensitive structures, but this can be mitigated by stereotactic magnetic resonance image guided adaptive radiation therapy (SMART).Methods and Materials: We describe our single-institution experience of high biologically effective dose SMART before resection of localized pancreatic adenocarcinoma. Toxicity was evaluated according to Common Terminology Criteria for Adverse Events (V 5.0). Tumor response was evaluated according to the College of American Pathologists tumor regression grading criteria.Results: We analyzed 26 patients with borderline resectable (80.8%), locally advanced (11.5%), and resectable (7.7%) tumors who received ablative dose SMART (A-SMART) followed by surgical resection. Median age at diagnosis was 68 years (range, 34-86). Most patients received chemotherapy (80.8%) before RT. All patients received A-SMART to a median dose of 50 (range, 40-50) Gy in 5 fractions. Toxicity data were collected prospectively and there were no acute grade 2+ toxicities associated with RT. The median time to resection was 50 days (range, 37-115), and the procedure types included Whipple (69%), distal (23%), or total pancreatectomy (8%). The R0 resection rate was 96% and no perioperative deaths occurred within 90 days. Pathologic response was observed in 88% of cases. The time from RT to surgery was associated with tumor regression grade (P = .0003). The median follow-up after RT was 16.5 months (range, 3.9-26.2). The derived median progression-free survival from RT was 13.2 months.Conclusions: The initial surgical and pathologic outcomes after A-SMART are encouraging. Preoperative A-SMART was associated with low toxicity rates and no surgical or RT-associated mortality. The surgical morbidity was comparable to historic rates after upfront resection. These data also suggest that the time from stereotactic body RT to surgical resection is associated with pathologic response.(c) 2022 The Authors. Published by Elsevier Inc. on behalf of American Society for Radiation Oncology. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Current guidelines recommend neoadjuvant therapy for pancreatic ductal adenocarcinoma (PDAC) patients with anatomically resectable tumors but elevated CA 19‐9. However, this recommendation is based on data from anatomically resectable and borderline resectable PDAC patients. Therefore, we analyzed the association of preoperative CA 19‐9 with oncologic outcomes in a cohort of anatomically resectable PDAC patients.