McWilliams, Robert R.

e16259 Background: Patients with KRAS mutant (mt) pancreatic ductal adenocarcinoma (PADC) have worse survival outcomes compared to KRAS wild-type (wt) PDAC patients. However, the prognostic implication of the KRAS mutation subtype (e.g. G12D, G12R, G12V and Q61) remains unclear. Furthermore, the clinical and molecular characteristics associated with these mutation subtypes remain not well defined. Methods: A retrospective review was conducted on patients with KRAS PDAC who underwent Next Generation Sequencing at Mayo Clinic between December 1, 2018 and December 1, 2021. Their somatic mutations, RNA expression, demographics, disease characteristics, therapies offered, and clinical outcomes were collected via chart review. Results on KRAS wt were reported previously; KRAS mt are reported here. Results: A total of 158 KRAS mt patients (at diagnosis: average age 63.8 years, 57% male, 88 (56%) Stage IV) were included. 10% of patients had KRAS Q61 mutation, 14% G12R, 30% G12V and 46% G12D. G12R had a longer overall survival (OS) compared to the others (median 24.8 vs 17.5 months, unadjusted hazard ratio (HR) 0.68, p=0.05), particularly in patients with localized disease at diagnosis (median 35.4 vs 28.3 months, p=0.08). Among patients with metastatic disease at diagnosis, G12V had the lowest OS (median 9.8 vs 12.4 months, unadjusted HR 1.8, p=0.02). 137 (87%) patients had at least one pathogenic somatic variant, with statistically significant differences in SMAD4, TP53, MYC, RB1, KMT2D, RBM10, RNF43, KDM6A, KMT2C, RBM10, LRP1B, PIK3CA, and SMARC among the KRAS mt subtypes. 82 (52%) patients had at least one RNA expression variant, with statistically significant differences in CCND1, CCNE1, HRAS, MET, EGFR, and ERB3 among KRAS mt subtypes. Between these subtypes, there were no statistically significant differences in TMB value, location of PDAC or subsequent metastasis, lines of treatment (average 2.3), age at diagnosis, or gender. Conclusions: KRAS mt subtypes may confer different PDAC phenotypes. In our cohort, G12R is associated with improved OS while G12V correlates with worse prognosis in de novo metastatic disease. Additionally, there are differences in genomic variations and RNA expression between the KRAS mt subtypes. To further examine this, transcriptomic analysis is underway. [Table: see text]

Abstract Purpose: Mucosal melanoma is a rare, aggressive form of melanoma with extremely high recurrence rates despite definitive surgical resection with curative intent. Currently there is no consensus on adjuvant therapy. Data on checkpoint inhibitors for adjuvant therapy are lacking. Patients and Methods: We performed a single-arm, multicenter clinical trial using “flip dose” ipilimumab (1 mg/kg q3w × 4 cycles), and nivolumab (3 mg/kg q3w × 4 cycles), then nivolumab 480 mg q4w × 11 cycles to complete a year of adjuvant therapy. Participants must have had R0/R1 resection ≤90 days before registration, no prior systemic therapy (adjuvant radiotherapy allowed), ECOG 0/1, and no uncontrolled autoimmune disease or other invasive cancer. Patients were recruited through the Midwest Melanoma Partnership/Hoosier Oncology Network. Results: From September 2017 to August 2021, 35 patients were enrolled. Of these, 29 (83%) had R0 resections, and 7 (20%) received adjuvant radiotherapy. Median age was 67 years, 21 (60.0%) female. Recurrence-free survival (RFS) rates at 1 and 2 years were 50% [95% confidence interval (CI), 31%–66%] and 37% (95% CI, 19%–55%), respectively. Overall survival rates at 1 and 2 years were 87% (95% CI, 68%–95%) and 68% (95% CI, 46%–83%), respectively. Median RFS was 10.3 months (95% CI, 5.7–25.8). Most common grade 3 toxicities were diarrhea (14%), hypertension (14%), and hyponatremia (11%), with no grade 4/5 toxicities. Conclusions: Flip-dose ipilimumab and nivolumab after resection of mucosal melanoma is associated with outcomes improved over that of surgical resection alone. Long-term follow-up, subgroup analyses and correlative studies are ongoing.

Importance Metastatic colorectal cancer (mCRC) with deficient DNA mismatch repair (dMMR) shows frequent and durable responses to programmed cell death 1 blockade. While most of these tumors are sporadic and observed in older patients, first-line pembrolizumab data are limited to findings from the KEYNOTE-177 trial (A Phase III Study of Pembrolizumab [MK-3475] vs Chemotherapy in Microsatellite Instability-High [MSI-H] or Mismatch Repair Deficient [dMMR] Stage IV Colorectal Carcinoma). Objective To investigate outcome with first-line pembrolizumab monotherapy in mostly older patients with dMMR mCRC at a multisite clinical practice. Design, Setting, and Participants This cohort study included consecutive patients with dMMR mCRC who received pembrolizumab monotherapy between April 1, 2015, and January 1, 2022, at Mayo Clinic sites and the Mayo Clinic Health System. Patients were identified from review of electronic health records at the sites, which included the evaluation of digitized radiologic imaging studies. Intervention Patients with dMMR mCRC received first-line pembrolizumab, 200 mg, every 3 weeks. Main Outcomes and Measures The primary study end point was progression-free survival (PFS), which was analyzed using the Kaplan-Meier method and a multivariable stepwise Cox proportional hazards regression model. Clinicopathological features, including metastatic site and molecular data ( BRAF V600E and KRAS ), were also analyzed along with tumor response rate, which was determined using Response Evaluation Criteria in Solid Tumors, version 1.1. Results The study cohort included 41 patients (median [IQR] age at treatment initiation, 81 [76-86] years; 29 females [71%]) with dMMR mCRC. Of these patients, 30 (79%) had the BRAF V600E variant and 32 (80%) were classified as having sporadic tumors. Median (range) follow-up was 23 (3-89) months. Median (IQR) number of treatment cycles was 9 (4-20). Overall response rate was 49% (20 of 41 patients), including 13 patients (32%) with complete responses and 7 (17%) with partial responses. Median (IQR) PFS was 21 (95% CI, 6-39) months. Liver as a site of metastasis was associated with significantly poorer PFS vs nonliver metastasis (adjusted hazard ratio, 3.40; 95% CI, 1.27-9.13; adjusted P = .01). Complete and partial responses were observed in 3 patients (21%) with liver metastasis vs 17 patients (63%) with nonliver metastases. Treatment-related grade 3 or 4 adverse events were observed in 8 patients (20%), 2 of whom discontinued therapy; there was 1 treatment-related death. Conclusions and Relevance This cohort study found a clinically significant prolongation of survival in older patients with dMMR mCRC who were treated with first-line pembrolizumab in routine clinical practice. Furthermore, liver vs nonliver metastasis was associated with poorer survival in this patient population, which suggests that the metastatic site has implications for survival outcome.

TPS780 Background: Pancreatic adenocarcinoma is an aggressive malignancy with a limited number of therapeutic options. One subset of patients (up to 15%) carries germline and/or somatic mutations in homologous recombination repair genes, most notably BRCA1, BRCA2 and PALB2 amongst others, that confer sensitivity to PARP inhibition. Combinations of PARP inhibitors with anti-PD1 immunotherapy have shown activity in breast and ovarian cancer and have not yet been thoroughly studied in pancreatic cancer. Methods: We designed a single-arm phase 2 investigator-initiated study utilizing the combination of niraparib, a highly selective PARP inhibitor and a dostarlimab, an anti PD1 antibody, in the subset of pancreatic cancer patients with germline or somatic mutations in BRCA1/2, PALB2, BARD1, RAD51C, or RAD51D. Additional inclusion criteria include metastatic pancreatic adenocarcinoma, receipt of a platinum agent in 1st or 2nd line unless contraindicated, and at least 1 but not more than 2 prior lines of systemic therapy not including maintenance. Prior PARP inhibition is allowed, but not immediately prior to enrollment. Exclusion criteria include active unstable autoimmune disease or prior malignancy requiring active treatment within 2 years. Patients are treated with niraparib 200 mg orally once daily on days 1 through 21 of a 21 day cycle. Dostarlimab is administered IV 500 mg every 3 weeks for the 1st 4 cycles and then 1000 mg IV every 6 weeks subsequently. The primary endpoint of the study is the disease control rate at 12 weeks using standard iRECIST criteria. Twenty patients will be enrolled to ensure 19 evaluable. The design has 80% power to detected improvement in disease control rate from 25-50% with significance level of 0.10. Descriptive factors include gene mutated for inclusion, germline/somatic, and platinum refractoriness. Given the size of the study along with genetic heterogeneity there will be no interim analysis. Patients are being enrolled at 3 Mayo clinic sites in Rochester Minnesota, Phoenix Arizona, Jacksonville Florida. To date, 13 patients have been enrolled across all 3 sites. Full accrual is anticipated by early 2023. Correlative studies include genomic characterization of baseline tumors, assessment of immune infiltration of tumor microenvironment, tumor collection for organoid/xenograft, and serial circulating cell-free DNA and immune biomarkers. Trial Identifiers: NCT04493060, Mayo: MC1841. Supported by Glaxo Smith Kline. Clinical trial information: NCT04493060 .

57 Background: Metastatic colorectal cancer (mCRC) with deficient DNA mismatch repair (dMMR) or microsatellite instability-high (MSI-H) show frequent and durable responses to programmed cell death -1 (PD-1) blockade. While the majority of these tumors are sporadics and observed in elderly patients, first-line data are limited to the KEYNOTE-177 study. Here, we report a consecutive series of elderly patients with dMMR mCRC treated with pembrolizumab in routine clinical practice that includes analysis of clinical outcome based on metastatic site. Methods: Patients with dMMR mCRC received first-line pembrolizumab (200 mg every 3 weeks) (N = 41) at Mayo Clinic and Mayo Clinic Health System (2015-2022). Clinicopathological features including metastatic site and molecular data ( BRAFV600E, KRAS) were analyzed in relationship to tumor response rate (RECIST version 1.1). Furthermore, these variables were also analyzed in relationship to patient progression-free survival (PFS) using Kaplan-Meier methodology and multivariable stepwise Cox regression. Results: Among patients with dMMR mCRC, 29/41 (70.7%) were female, 30 (78.9%) harbored BRAFV600E, and 32 (80%) were sporadic. Median age at start of treatment was 80.6 years (IQR of 75.9, 85.9) and median number of treatment cycles was 9 (IQR: 4, 20). At a median follow-up of 23 months (range, 3.0 to 88.5), patient median PFS was 21.3 months (95% CI: 6.4, 38.5). An overall response was observed in 48.8% (20 of 41) of patients including 13 (31.7%) complete (CR) and 7 (17.1%) partial responses (PR). The median duration of response was 42.2 months (95%CI: 8.6, NR). Patients with metastases that included liver had significantly poorer PFS compared to those with non-liver metastases (HRadj 3.40 (95%CI: 1.27-9.13); Padj= 0. 01). In this regard, responses (CR, PR) to pembrolizumab were observed in 3 (21.4%) patients with liver metastasis compared to 17 (62.9%) of those with non-liver metastases. Treatment-related grade 3 or 4 adverse events were observed in 9 (22.0%) patients of whom two discontinued therapy, and there was one treatment-related death. Conclusions: First-line therapy with pembrolizumab for dMMR mCRC significantly prolonged survival in an elderly patient population with manageable toxicity in routine clinical practice. Moreover, the survival benefit of pembrolizumab was significantly attenuated in patients with liver vs non-liver metastases.

424 Background: Understanding the impact of anticancer therapies on immune system is critical to successful design and incorporation of immunotherapies. We developed a novel immune monitoring platform that measures the relative amount of circulating effector T cells and antitumor cytotoxicity of circulating immune cells. We previously showed that this assay can differentiate patients’ clinical response to anti-PD-1 therapy. Here, we applied this assay to patients with gastric or gastroesophageal junction adenocarcinoma (GGEA) who received chemoradiation or chemotherapy-based therapies. Methods: Patients underwent peripheral blood collection at baseline and during follow-up. Levels of circulating effector T cells (CX3CR1+NKG7+/CD3+CD8+) were quantified by flow cytometry using peripheral blood mononuclear cells (PBMCs). Antitumor cytotoxicity of circulating immune cells was evaluated by co-culturing CD3/CD28 activated PBMCs with calcein-AM labeled GGEA tumor cells (FLO-1). Antitumor cytotoxicity of individual patients’ PBMCs was calculated based on the amount of calcein released by dead tumor cells. Results: In a pilot study of 8 patients with mismatch repair-proficient (pMMR) GGEA, the changes in the frequency of effector T cells appeared to be associated with radiographic response to treatment based on RECIST (3 partial response [PR], 3 stable disease [SD], and 2 progressive disease [PD]). The median interval between sequential blood collections was 64 days and an increase in effector T cells was observed in patients with PD. Antitumor cytotoxicity was evaluated in 4 patients who did not receive targeted therapies or immune checkpoint inhibitors. Two of these patients (a, b) had blood collected at the time of diagnosis (treatment naïve) and after neoadjuvant therapy. One developed pulmonary metastases after chemoradiation while the other had significant tumor shrinkage after chemotherapy. The decrease in antitumor cytotoxicity of PBMCs was less in the patient with PD (-19.4%) than the one with PR (-48.5%). Two patients (c, d) had blood collected twice while receiving the same chemotherapy for metastatic disease (not treatment naïve). The decrease in antitumor cytotoxicity of PBMCs was less in the patient with SD (-0.3%) than the one with PR (-14.5%). Conclusions: We demonstrated the feasibility of using PBMCs to monitor immune response to anticancer therapies. Our data raise the possibility that the amount of circulating effector T cells and antitumor cytotoxicity of PBMCs may be associated with tumor burden in patients with pMMR solid tumors. [Table: see text]

227 Background: Circulating tumor DNA (ctDNA) consists of small fragments of DNA released into the plasma from cancer cells. Tumor informed ctDNA testing by whole exome sequencing of the primary tumor coupled with multiplex polymerase chain reaction (PCR)-based next generation sequencing of cell free DNA in serum, can detect and quantify ctDNA, allowing for detection of minimal residual disease (MRD). Methods: We conducted a retrospective analysis of 120 patients with colorectal cancer who had at least one tumor-informed ctDNA MRD assay completed between May 6, 2019, and July 1, 2022, at Mayo Clinic, Rochester. Disease recurrence was defined as radiographic evidence consistent with recurrence with or without biopsy confirmation. Data are presented descriptively, including number of ctDNA assays completed, ctDNA positivity prior to disease recurrence, and ctDNA concordance with carcinoembryonic antigen (CEA). The study protocol was exempt after review by the Mayo Clinic Institutional Review Board. Results: One-hundred twenty patients were included in the study with median age at initial disease diagnosis of 67.0 years. Sixty-four percent were male and 94% were white. At time of initial diagnosis, 10 had stage I, 23 stage II, 60 stage III, and 25 stage IV disease. In 120 patients, 476 ctDNA assays were performed, and 110 recurrences were observed among 62 patients. There were 39 instances in which ctDNA was obtained prior to clinical detection of recurrence and of these, at least one ctDNA assay was positive in 28 cases (72%). CEA was obtained prior to recurrence in 88 instances and was elevated in only 39 cases (44%). Among 37 instances where both ctDNA and CEA testing were obtained prior to recurrence, ctDNA was positive in 27 cases (73%) while CEA was positive in 14 cases (38%). ctDNA was positive in 83% of recurrences involving liver and 62.5% of recurrences involving only the lungs. ctDNA and CEA positivity are shown by location of recurrence. ctDNA and CEA were discordant in 44% of instances in which the assays were completed within 2-weeks of each other. Results of a ctDNA assay impacted management decisions in 16% of cases. Conclusions: ctDNA detected 72% of recurrences with higher rates of detection in liver versus lung metastasis. ctDNA performed superiorly to serum CEA in detection of recurrence, suggesting a role in disease surveillance. However, ctDNA impacted disease management in only 16% of patients, suggesting need for better patient selection and further study for ctDNA-based disease management strategy (more details will be reported). [Table: see text]