Mitchell, Jessica L.

PURPOSE Immunotherapy has demonstrated limited efficacy in the treatment of microsatellite-stable (MSS) metastatic colorectal cancer (mCRC) to date. We evaluated whether an off-the-shelf, multipeptide vaccine, PolyPEPI1018, in conjunction with standard chemotherapy can induce broad antitumor immune responses, potentially improving disease control in refractory mCRC. PATIENTS AND METHODS This single-arm, open-label study enrolled adults with MSS mCRC who had progressed after ≤2 previous lines of therapy for metastatic disease. PolyPEPI1018 was administered subcutaneously to four anatomical sites on days 1 and 15 and TAS-102 orally twice a day on days 1-5 and 8-12 of a 28-day cycle. Patients were treated for seven cycles or until disease progression. The primary end point was safety. Secondary end points were overall response rate, progression-free survival (PFS), overall survival (OS), and immune and genetic correlates. RESULTS Fifteen patients were enrolled; 80% had liver metastases and 67% had KRAS mutations. Adverse events (AEs) related to PolyPEPI1018 were grade 1 and 2 local skin reactions (n = 14). Grade 3 AEs (n = 15) at least possibly related to treatment were fatigue, decreased lymphocyte and neutrophil counts, and diarrhea. None had objective tumor response; the disease control rate was 53.3%. The median PFS (mPFS) was 4.0 (95% CI, 2.2 to 6.1) months and the median OS (mOS) was 8.7 (95% CI, 6.4 to 15.2) months. In post hoc subgroup analyses, patients without active liver metastasis had improved mPFS of 9.7 months and mOS of 14.8 months. In addition, patients who were predicted to have broader immune responses to vaccine based on human leukocyte antigen genotype had longer mOS (10.3 v 4.6 months, hazard ratio, 0.29 [95% CI, 0.07 to 1.17]). CONCLUSION The addition of PolyPEPI1018 to TAS-102 was safe and induced immunological responses that were associated with improved clinical outcomes. Further investigation of this chemo-immunotherapeutic is warranted.

84 Background: Local therapies potentially offer a curative approach for patients with oligometastatic colorectal cancer (CRC). The effectiveness of systemic chemotherapy following definitive local treatment in this setting is not well-defined. Tumor-informed circulating tumor DNA (ctDNA) might guide management strategies after curative-intent local treatment. Methods: This is a single institution retrospective study of patients with CRC who underwent curative-intent local therapy to an isolated site of metastatic disease and had post-intervention tumor-informed ctDNA (Signatera) testing. The study was approved by the institutional review board. Clinical characteristics, including ctDNA results, were collected and evaluated. Kaplan-Meier method and log-rank test were used to calculate and compare disease-free survival (DFS). Factors associated with DFS were analyzed using multivariate Cox proportional hazards model. Results: 45 patients were included with median age of 59 years, 62% being male, 91% white, and 53% with stage IV disease at diagnosis. 37% of the patients had RAS mutations, no patient had BRAF mutation, and 2.2% patient had mismatch repair deficient disease. Isolated liver metastases were present in 80% of patients, lung metastases in 11% and other sites in 9%. 44 patients received chemotherapy prior to definitive treatment, with a median treatment duration of 16 weeks. ctDNA tests were done prior to local therapy in 23 patients, with 14 cases (61%) testing positive. Definitive treatment included resection (58%), ablation (13%), radiotherapy (4%), and multimodality (25%). Post-definitive treatment chemotherapy was administered to 24 (53%) patients. ctDNA positivity following definitive therapy was observed in 10 patients (22%), which was associated with a poorer prognosis, with a median DFS of 5.3 months compared to 21.3 months for the ctDNA-negative group (p<0.001). These findings were confirmed on multivariate analysis. In patients who had negative ctDNA after definitive local treatment, median DFS was 14.9 months for those who received post-intervention chemotherapy versus 21.3 months for those without post-intervention chemotherapy (p=0.835). Conclusions: Patients with negative ctDNA results following definitive local therapy for isolated metastatic CRC have better prognosis. Post-intervention chemotherapy in this group of patients was not associated with improved DFS. ctDNA guided omission of post-intervention chemotherapy following curative-intent local treatment of oligometastatic CRC warrants further study. [Table: see text]

(1) Background: Local therapies offer a potentially curative approach for patients with oligometastatic colorectal cancer (CRC). An evidence-based consensus recommendation for systemic therapy following definitive locoregional therapy is lacking. Tumor-informed circulating tumor DNA (ctDNA) might provide information to help guide management in this setting. (2) Methods: A multi-institutional retrospective study was conducted, including patients with CRC that underwent curative-intent locoregional therapy to an isolated site of metastatic disease, followed by tumor-informed ctDNA assessment. The Kaplan–Meier method and log-rank tests were used to compare disease-free survival based on ctDNA results. ctDNA test performance was compared to carcinoembryonic antigen (CEA) test results using McNemar’s test. (3) Results: Our study cohort consisted of 87 patients treated with locoregional interventions who underwent ctDNA testing. The initial ctDNA test post-intervention was positive in 28 patients and negative in 59 patients. The median follow-up time was 14.0 months. Detectable ctDNA post-intervention was significantly associated with early disease recurrence, with a median disease-free survival (DFS) of 6.63 months compared to 21.30 months in ctDNA-negative patients (p < 0.001). ctDNA detected a numerically higher proportion of recurrences than CEA (p < 0.097). Post-intervention systemic therapy was not associated with improved DFS (p = 0.745). (4) Conclusions: ctDNA results are prognostically important in oligometastatic CRC, and further prospective studies are urgently needed to define its role in guiding clinical decisions.

26 Background: Local therapies have the potential to cure a portion of patients with colorectal cancer with liver-only metastatic disease (CRLM). Peri-operative chemotherapy has not been shown to improve overall survival when added to local therapy in CRLM. Circulating-tumor DNA (ct-DNA) may have potential to help guide management decisions following local therapy. Methods: We conducted a retrospective analysis of health records of CRLM patients who had tumor-informed ct-DNA (Signatera) measurement following curative-intent local therapy prior to August 30th, 2023. Disease-free survival (DFS) was defined as the time from ct-DNA test until radiographic evidence of disease. Descriptive characteristics of the cohort, ct-DNA results and their impact on adjuvant therapy decisions were recorded. Survival analysis was carried out using R software v4.3.1 with survival and survminer packages. The Kaplan–Meier method was used to estimate the survival distribution. Log-rank test was used for comparison. A multivariable Cox proportional hazards model was used to assess prognostic factors associated with DFS ( coxph). Results: 27 patients with CRLM underwent local therapy followed by ct-DNA collection. The median age was 61 years, 67% were male, and 85% were White. Molecular characteristics: KRAS 31%, NRAS/BRAF 0%, microsatellite instability 4%. The median time from initial diagnosis to treatment of liver disease was 21.0 months. 63% of patients received less than 6 months of systemic therapy prior to local therapy. ct-DNA was checked prior to definitive therapy in 12 cases and was positive in 5 cases (detection rate of 42%). Liver-directed therapy involved: resection (n=15), ablation (6), radiation (2) or a combination (4). The median follow-up time from liver-directed therapy was 13.2 months. Post-local therapy chemotherapy was initiated prior to recurrence in 59% of cases. ct-DNA results contributed to immediate post-management decisions in 15% of cases. There were 14 radiographic recurrences (11 to liver only, 3 to other sites). Positive ct-DNA on initial testing following local therapy was associated with poorer DFS in univariate analysis and was the only prognostic factor identified on multivariable analysis. Conclusions: ct-DNA positivity following local therapy for CRLM is associated with earlier recurrence. Baseline testing before local therapy may be important for interpretation of testing results post-local therapy, given frequent missed disease detection. Additional clinical trial data is needed to explore ct-DNA-guided treatment decisions in CRLM. [Table: see text]

PURPOSE Recurrence after curative-intent treatment occurs in 20%-50% of patients with stage II-IV colorectal cancer (CRC), underscoring the need for early detection of minimal residual disease (MRD) using circulating tumor DNA (ctDNA). Here, we examined the pattern of use of a tumor-informed ctDNA assay in CRC MRD monitoring in routine clinical practice at Mayo Clinic, Rochester. METHODS We conducted a retrospective analysis of health records of patients with CRC who had at least one tumor-informed ctDNA assay from May 2019 through July 1, 2022. Recurrence was defined as radiographic evidence of disease. Descriptive characteristics of the cohort, ctDNA results, and subsequent interventions were recorded. RESULTS Of the 120 patients included, the median age at diagnosis was 67 years, 46% were female, and 94% were White. At diagnosis, 10 patients had stage I, 23 stage II, 60 stage III, and 25 stage IV disease. Of 476 ctDNA assays performed, 70% were performed in patients who had recurrent disease most commonly to monitor the effectiveness of therapeutic interventions and 16% resulted in a change in clinical decision making. There were 110 recurrences identified in 62 patients, as some patients experienced more than one recurrence over time. Compared with serum carcinoembryonic antigen levels, ctDNA results correlated better with radiologic imaging. CONCLUSION Routine ctDNA monitoring for MRD detection has been adopted in clinical practice; however, 84% of ctDNA assays performed did not result in a change in clinical management. This suggests the need for further clinical research data to guide routine clinical use of ctDNA MRD testing in CRC.

Over the past 20 years, rates of early-onset colorectal cancer (eoCRC), defined as <50 years of age at diagnosis, have increased, with 16–25% associated with a pathogenic germline variant (PGV) resulting in a hereditary cancer syndrome. In the present study, we sought to further characterize PGVs observed in patients with eoCRC. We conducted a retrospective analysis of patients with a history of CRC referred for genetic counseling at Mayo Clinic Rochester between April 2019 and April 2022. Three hundred and three CRC patients were referred to medical genetics, including 124 with a history of eoCRC. Only 84 patients (68%) with eoCRC referred for genetic counseling completed genetic testing, with an average of 48 genes evaluated. PGVs were identified in 27.4% with eoCRC, including 8.3% with Lynch syndrome (LS). Other detected PGVs known to increase the risk of CRC included MUTYH (4.8%), CHEK2 (3.6%), APC, BMPR1A, and TP53 (1.3% each). Among those with aoCRC, 109 patients (61%) completed genetic testing, among which 88% had either a dMMR tumor, personal history of an additional LS malignancy, or family history of LS malignancy, with PGVs detected in 23% of patients. This study reinforces the importance for all patients with CRC, especially those with eoCRC, to undergo germline testing.

3595 Background: PolyPEPI1018 is an off-the-shelf, multi-peptide vaccine containing 12 immunogenic epitopes derived from 7 tumor-specific antigens frequently expressed in patients with mCRC. Following early evidence of clinical activity of PolyPEPI1018 in first-line MSS mCRC, here we report the results of a phase Ib study of PolyPEPI1018 vaccine plus trifluridine/tipiracil (TAS-102) in late-stage mCRC patients. Methods: Patients with MSS mCRC who have progressed on ≤2 lines of prior chemotherapy regimen for mCRC received PolyPEPI1018 subcutaneously on days 1 and 15 and TAS-102 orally twice daily on days 1-5 and 8-15 of a 28-day cycle. Treatment continued for up to 7 cycles, until disease progression or unacceptable toxicity. Immunomonitoring was performed at both blood and tumor levels prior to and on study treatment. The primary endpoint of the study was safety and tolerability. Data on objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS) and correlation studies will be presented. Results: 15 patients started treatment. Median age was 55 years (range 31–71), 73% had liver metastases (mets), 73% had KRAS mutant tumors. The most common side effect related to PolyPEPI1018 was Grade (Gr) 1-2 local skin reactions in 93% of patients. Gr 3 events (n = 15) at least possibly related to treatment were fatigue, decreased white blood cell, lymphocyte and neutrophil counts, nausea, diarrhea, myalgia, and maculo-papular rash. There were no Gr 4 or 5 events. The ORR was 0%. The DCR was 53.3% in the overall population and 36% and 100% for the patients with liver mets and without liver mets, respectively. The mPFS was 4 months (95%CI 2.2-6.1) in the overall population and 2.3 months (95%CI 2.1-NE) and 7.6 months (95%CI 4.4-NE) for the patients with liver mets and without liver mets, respectively (HR = 5.73 (95%CI 1.21, 27.06); p = 0.015). At the data cut-off date (Feb 10, 2023), the mOS was 8.7 months (95%CI 6.9-NE; not mature) in the overall population and it was not reached in patients without liver mets. Patients with increased PFS (≥ 24 weeks) had more robust vaccine-specific humoral and T cell responses induced by higher number of vaccine peptides than patients with PFS < 24 weeks. Conclusions: To our knowledge, this is the first study investigating combination of a cancer vaccine with TAS-102 chemotherapy in advanced MSS mCRC. Our results show that PolyPEPI1018 plus TAS-102 was well-tolerated with few grade 3 AEs beyond what is expected with TAS-102 monotherapy. Despite no objective tumor responses could be detected, correlative data suggest contribution of PolyPEPI1018-induced immunological responses to the improved clinical benefit and the combination warrants further testing. Clinical trial information: NCT05130060 .

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]

147 Background: PolyPEPI1018 is an off-the-shelf, multi-peptide vaccine containing 12 immunogenic epitopes derived from 7 cancer testis antigens (CTAs) frequently expressed in patients with colorectal cancer (CRC). PolyPEPI1018 successfully induced anticancer immunity and triggered recruitment and infiltration of cytotoxic T cells into the tumor of MSS mCRC subjects demonstrating also early evidence of clinical activity, in first-line mCRC. Here we report the initial results of the phase Ib study of PolyPEPI1018 vaccine plus trifluridine/tipiracil (TAS-102) in late-stage mCRC patients. Methods: Patients with MSS mCRC who have progressed on ≤2 lines of prior chemotherapy regimen for mCRC received PolyPEPI1018 subcutaneously on days 1 and 15 and TAS-102 orally twice daily on days 1-5 and 8-12 of a 28-day cycle. Treatment continued for up to 7 cycles until disease progression or unacceptable toxicity. Immunomonitoring was performed at both blood and tumor levels prior to- and on study treatment. The primary endpoint of the study was safety and tolerability. Data on objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS) and correlation studies will be also presented. Results: 15 patients (67% male) started treatment. At baseline, median age was 55 years (range 31–71), 73% had liver metastases and the primary tumor site was colon-sigmoid in 40% and rectum in 33%. The combination was well-tolerated; most common side effect related to PolyPEPI1018 was Grade (Gr) 1-2 local skin reactions in 93% of patients. Gr 3 events. There were no Gr 4 or 5 events. The ORR was 0% and the DCR was 50%. The mPFS was 2.5 months (95%CI 2.1-NR). At the data cut-off (September 7, 2022), the mOS has not been reached; median follow-up was 4.0 months (95% CI 2.2-4.4). Post-treatment, vaccine-specific T cell responses were detected ex vivo in the PBMC of 4/5 subjects tested. In addition, one subject who had no detectable T cell response at peripheral level, responded at the tumor level with more than 300% increase of both CD3+ and CD8+ tumor-infiltrating lymphocytes compared to baseline. Patients with increased PFS (≥ 16 weeks) had robust vaccine-specific T cell responses. Conclusions: To our knowledge, this is the first phase Ib study investigating combination of a cancer vaccine with TAS-102 chemotherapy in advanced MSS mCRC. Our results show that PolyPEPI1018 plus TAS-102 was well-tolerated with few grade 3 AEs beyond what is expected with TAS-102 monotherapy. PolyPEPI1018 induced immunological responses at both peripheral and tumor level, albeit no objective tumor responses could be detected. The study is on-going for the collection of overall survival data. Clinical trial information: NCT05130060 .

Abstract Purpose: Although chemotherapy is standard of care for metastatic colorectal cancer (mCRC), immunotherapy has no role in microsatellite stable (MSS) mCRC, a “cold” tumor. PolyPEPI1018 is an off-the-shelf, multi-peptide vaccine derived from 7 tumor-associated antigens (TAA) frequently expressed in mCRC. This study assessed PolyPEPI1018 combined with first-line maintenance therapy in patients with MSS mCRC. Patients and Methods: Eleven patients with MSS mCRC received PolyPEPI1018 and Montanide ISA51VG adjuvant subcutaneously, combined with fluoropyrimidine/biologic following first-line induction with chemotherapy and a biologic (NCT03391232). In Part A of the study, 5 patients received a single dose; in Part B, 6 patients received up to three doses of PolyPEPI1018 every 12 weeks. The primary objective was safety; secondary objectives were preliminary efficacy, immunogenicity at peripheral and tumor level, and immune correlates. Results: PolyPEPI1018 vaccination was safe and well tolerated. No vaccine-related serious adverse event occurred. Eighty percent of patients had CD8+ T-cell responses against ≥3 TAAs. Increased density of tumor-infiltrating lymphocytes were detected post-treatment for 3 of 4 patients’ liver biopsies, combined with increased expression of immune-related gene signatures. Three patients had objective response according to RECISTv1.1, and 2 patients qualified for curative surgery. Longer median progression-free survival for patients receiving multiple doses compared with a single dose (12.5 vs. 4.6 months; P = 0.017) suggested a dose–efficacy correlation. The host HLA genotype predicted multi-antigen–specific T-cell responses (P = 0.01) indicative of clinical outcome. Conclusions: PolyPEPI1018 added to maintenance chemotherapy for patients with unresectable, MSS mCRC was safe and associated with specific immune responses and antitumor activity warranting further confirmation in a randomized, controlled setting.