Comprehensive Landscape of BRAF Variant Classes, Clonalities, and Co-Mutations in Metastatic Colorectal Cancer Using ctDNA Profiling

Although V600E accounts for the majority of the BRAF mutations in metastatic colorectal cancer (mCRC), non-V600 BRAF variants have been shown in recent years to represent a distinct molecular subtype. This study provides a comprehensive profile of BRAF variants in mCRC using a large genomic database of circulating tumor DNA (ctDNA) and analyzing clinical outcomes in a cohort of patients with atypical (non-V600) BRAF variants (aBRAF; class II, class III, unclassified). Overall, 1733 out of 14,742 mCRC patients in the ctDNA cohort had at least one BRAF variant. Patients with atypical BRAF variants tended to be younger and male. In contrast to BRAFV600E, BRAF class II and III variants and their co-occurrence with KRAS/NRAS mutations were increased at baseline and especially with those patients predicted to have prior anti-EGFR exposure. Our clinical cohort included 38 patients with atypical BRAF mCRC treated at a large academic referral center. While there were no survival differences between atypical BRAF classes, concurrent RAS mutations or liver involvement was associated with poorer prognosis. Notably, patients younger than 50 years of age had extremely poor survival. In these patients, the high-frequency KRAS/NRAS co-mutation and its correlation with poorer prognosis underlines the urgent need for novel therapeutic strategies. This study represents one of the most comprehensive characterizations to date of atypical BRAF variants, utilizing both ctDNA and clinical cohorts.

Mechanisms of resistance to EGFR-targeted therapies in colorectal cancer: more than just genetics

The development of acquired resistance to anti-EGFR therapies remains poorly understood, with most research to date exploring, and trying to overcome, various genomic mechanisms of resistance. However, recent work supports a model of resistance whereby transcriptomic mechanisms of resistance predominate in the presence of active cytotoxic chemotherapy combined with anti-EGFR therapy in the first-line setting, with a greater predominance of acquired MAPK mutations after single-agent anti-EGFR therapy in the later-line setting. The proposed model has implications for prospective studies evaluating anti-EGFR rechallenge strategies guided by acquired MAPK mutations and highlights the need to address transcriptional mechanisms of resistance.

Transcriptional Profiling and Consensus Molecular Subtype Assignment to Understand Response and Resistance to Anti-Epidermal Growth Factor Receptor Therapy in Colorectal Cancer

PURPOSE

Activating mutations in KRAS, NRAS, and BRAF are known to cause resistance to anti-epidermal growth factor receptor (EGFR) therapy; however, only approximately 40% of patients with colorectal cancer (CRC) with RASWT tumors respond to anti-EGFR treatment. We sought to discover novel biomarkers to predict response to anti-EGFR antibody treatment in CRC and to understand mechanisms of resistance to anti-EGFR therapy.

MATERIALS AND METHODS

Transcriptomic profiles from three clinical and two preclinical cohorts treated with cetuximab were used to assign consensus molecular subtypes (CMS) to each sample and correlated with outcomes.

RESULTS

Restricting to RASWT patients, we observed that CMS2 tumors (canonical subtype) had significantly higher response rates relative to other CMS when treated with cetuximab combination with doublet chemotherapy (Okita et al cohort: 92% disease control rate (DCR) for CMS2, chi-square P = .04; CALGB/SWOG 80405 cohort: 90% objective response rate (ORR) for CMS2, chi-square P < .001) and with single-agent cetuximab (68%, chi-square P = .01). CMS2 tumors showed best response among right-sided (ORR = 80%) and left-sided (ORR = 92%) tumors in the CALGB/SWOG 80405 cohort. CMS2 cells lines were most likely to be sensitive to cetuximab (60%) and CMS2 patient-derived xenograft had the highest DCR (84%). We found Myc, E2F, and mammalian target of rapamycin pathways were consistently upregulated in resistant samples (enrichment score >1, false discovery rate <0.25). Inhibitors of these pathways in resistant cell lines exhibited additive effects with cetuximab.

CONCLUSION

These data suggest that CRC transcriptional profiles, when used to assign CMS, provide additional ability to predict response to anti-EGFR therapy relative to using tumor sidedness alone. Notably both right-sided and left-sided CMS2 tumors had excellent response, suggesting that anti-EGFR therapy be included as a treatment option for right-sided CMS2 tumors.

Prospective Study of Perioperative Circulating Tumor DNA Dynamics in Patients Undergoing Hepatectomy for Colorectal Liver Metastases

OBJECTIVE

To evaluate the association of perioperative ctDNA dynamics on outcomes after hepatectomy for CLM.

SUMMARY BACKGROUND DATA

Prognostication is imprecise for patients undergoing hepatectomy for CLM, and ctDNA is a promising biomarker. However, clinical implications of perioperative ctDNA dynamics are not well established.

METHODS

Patients underwent curative-intent hepatectomy after preoperative chemotherapy for CLM (2013-2017) with paired prehepatectomy/postoperative ctDNA analyses via plasma-only assay. Positivity was determined using a proprietary variant classifier. Primary endpoint was recurrence-free survival (RFS). Median follow-up was 55 months.

RESULTS

Forty-eight patients were included. ctDNA was detected before and after surgery (ctDNA+/+) in 14 (29%), before but not after surgery (ctDNA+/-) in 19 (40%), and not at all (ctDNA-/-) in 11 (23%). Adverse tissue somatic mutations were detected in TP53 (n = 26; 54%), RAS (n = 23; 48%), SMAD4 (n = 5; 10%), FBXW7 (n = 3; 6%), and BRAF (n = 2; 4%). ctDNA+/+ was associated with worse RFS (median: ctDNA+/+, 6.0 months; ctDNA+/-, not reached; ctDNA-/-, 33.0 months; P = 0.001). Compared to ctDNA+/+, ctDNA+/- was associated with improved RFS [hazard ratio (HR) 0.24 (95% confidence interval (CI) 0.1-0.58)] and overall survival [HR 0.24 (95% CI 0.08-0.74)]. Adverse somatic mutations were not associated with survival. After adjustment for prehepatectomy chemotherapy, synchronous disease, and ≥2 CLM, ctDNA+/- and ctDNA-/- were independently associated with improved RFS compared to ctDNA+/+ (ctDNA+/-: HR 0.21, 95% CI 0.08-0.53; ctDNA-/-: HR 0.21, 95% CI 0.08-0.56).

CONCLUSIONS

Perioperative ctDNA dynamics are associated with survival, identify patients with high recurrence risk, and may be used to guide treatment decisions and surveillance after hepatectomy for patients with CLM.

Survival improvement for patients with metastatic colorectal cancer over twenty years

Over the past two decades of successive clinical trials in metastatic colorectal cancer (CRC), the median overall survival of both control and experimental arms has steadily improved. However, the incremental change in survival for metastatic CRC patients not treated on trial has not yet been quantified. We performed a retrospective review of 1420 patients with de novo metastatic CRC who received their primary treatment at the University of Texas M.D. Anderson Cancer Center (UTMDACC) from 2004 through 2019. Median OS was roughly stable for patients diagnosed between 2004 and 2012 (22.6 months) but since has steadily improved for those diagnosed in 2013 to 2015 (28.8 months), and 2016 to 2019 (32.4 months). Likewise, 5-year survival rate has increased from 15.7% for patients diagnosed from 2004 to 2006 to 26% for those diagnosed from 2013 to 2015. Notably, survival improved for patients with BRAFV600E mutant as well as microsatellite unstable (MSI-H) tumors. Multivariate regression analysis identified surgical resection of liver metastasis (HR = 0.26, 95% CI, 0.19-0.37), use of immunotherapy (HR = 0.44, 95% CI, 0.29-0.67) and use of third line chemotherapy (regorafenib or trifluridine/tipiracil, HR = 0.74, 95% CI, 0.58-0.95), but not year of diagnosis (HR = 0.99, 95% CI, 0.98-1), as associated with better survival, suggesting that increased use of these therapies are the drivers of the observed improvement in survival.

Abstract PR005: Outcomes in colitis-associated metastatic colorectal cancer and intersection with early-onset and signet ring cell carcinoma

Patients with inflammatory bowel disease (IBD) have a higher risk of developing colorectal cancer (CRC) and mortality from colitis-associated CRC (CA-CRC) is currently rising. Clinical and molecular differences between CA-CRC and sporadic-CRC (S-CRC) have been previously identified, however there are conflicting reports on outcomes of CA-CRC, especially for those with metastatic CRC (mCRC). Due to the earlier onset of CA-CRC, undiagnosed IBD has been speculated to be a contributing factor to the rising prevalence of early-onset CRC (EOCRC), but confirmatory studies are lacking. In this retrospective study, three independent CRC patient datasets from MDACC were used – the mATTACC discover cohort (n=32 CA-mCRC; n=425 S-mCRC), a tumor registry (n=1696, excluding MSI-High samples), and a real-world evidence (RWE) validation dataset (n=269 CA-mCRC; n=29,596 S-mCRC). These cohorts were analyzed in order to explore characteristics of patients with CA-mCRC, evaluate the amount of EOCRC attributable to CA-mCRC, and compare outcomes of patient populations with CA-mCRC. Median age at diagnosis for patients with CA-mCRC (48yo) was significantly lower compared to S-mCRC (58yo; p&lt;0.001), and an association between CA-mCRC and EOCRC was confirmed (OR=4.04, p&lt;0.001). Prevalence of signet ring cell and mucinous (SRC/M) histology, a rare subtype of CRC, was analyzed within CA-mCRC and EOCRC cases in our cohorts. SRC/M histology was present in 28%-39% of CA-mCRC and 13%-15% of EOCRC cases, thus confirming the strong association of SRC/M histology with both CA-mCRC (OR=3.13, p&lt;0.001) and EOCRC (OR=1.35, p&lt;0.001). Therefore, by comparing the frequency of SRC/M in EOCRC and late-onset CRC, and correcting by the proportion of CA-mCRC cases with SRC/M histology, we estimate between 8.3% to 10.2% of EOCRC may be due to undiagnosed or subclinical IBD. Median overall survival (mOS) for patients with CA-mCRC (31m) was lower relative to S-mCRC (39m; HR=1.26, 95%CI: 1.06-1.48). In EOCRC, patients with CA-mCRC had worse outcomes (mOS=25m) compared to S-mCRC (40m; HR=1.61, 95%CI: 1.23-2.11). Prevalence of SRC/M histology stratified by CA-mCRC or EOCRC status revealed an increasing trend of SRC/M occurrence specifically within CA-mCRC (1995-2015). Additionally, for patients with CA-mCRC the mOS for those with SRC/M (21m) was lower than those with mucinous (51m) histology, highlighting the poor prognosis of SRC/M in this patient population (HR=1.89, 95%CI: 1.06-3.33). Patients with CA-mCRC have worse outcomes than S-mCRC, and those with early-onset or SRC/M have lower survival rates. Tumor biology consistent with CA-CRC, including SRC/M histology, may be present in 8.3%–10.2% of patients with EOCRC without a clinical diagnosis of IBD. Although other confounding biology may be underlying this association, recognition of undiagnosed IBD in mCRC patients is important as it may impact prognosis and treatment strategies for this high-risk patient population.

Citation Format: Oscar E. Villarreal, Fadl Zeineddine, Ray Chacko, Christine Parseghian, Benny Johnson, Jason Willis, Michael Lee, Van Karlyle Morris, Arvind Dasari, Kanwal Raghav, Michael Overman, Y. Nancy You, Yinghong Wang, Dipen Maru, John Paul Shen, Scott Kopetz. Outcomes in colitis-associated metastatic colorectal cancer and intersection with early-onset and signet ring cell carcinoma [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer; 2022 Oct 1-4; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_1):Abstract nr PR005.

Abstract A023: Influence of pre-diagnosis obesity and post-diagnosis aspirin use on survival from stage IV colorectal cancer

Background: The relationship between obesity and colorectal cancer (CRC) outcome is poorly understood in late-stage patients. Increased body mass may negate aspirin use for cancer prevention, but the influence of body mass index (BMI) on post-diagnosis aspirin use is unclear. This study aims to evaluate impacts of pre-diagnosis BMI and post-diagnosis aspirin use on overall survival in late-stage CRC patients on the Assessment of Targeted Therapies Against Colorectal Cancer (ATTACC) clinical protocol. Methods: Patients with metastatic or treatment refractory disease were consented on the ATTACC protocol at MD Anderson Cancer Center and invited to complete a survey on risk factors relevant to CRC etiology. Using survey data, BMI was calculated from the decade prior to initial CRC diagnosis for 656 patients. Survival was measured from stage IV diagnosis until death or last follow-up. Cox Proportional Hazards models were constructed to estimate associations of pre-diagnosis obesity and post-diagnosis aspirin use with overall survival. Results: Controlling for age, sex, race, stage at initial diagnosis, and weight change between pre-diagnosis and survey date, patients with pre-diagnosis obesity had significantly higher likelihood of death (HR 1.45, 95% CI: 1.11, 1.91) compared to those with normal pre-diagnosis BMI. Further, only patients with normal weight pre-diagnosis experienced a survival benefit with post-diagnosis aspirin use (HR 0.59, 95% CI: 0.39, 0.90). Conclusions: Our findings suggest potentially differential tumor development resulting from the long-term physiologic host environment, here obesity. Confirmation and further evaluation are needed to determine whether pre-diagnosis BMI may predict benefit from post-diagnosis aspirin use.

Citation Format: Jennifer S. Davis, Janelle C. Chavez, Melissa Kok, Yazmin San Miguel, Hwa Young Lee, Henry Henderson, Michael J. Overman, Van Karlyle Morris, Bryan Kee, David Fogelman, Shailesh M. Advani, Benny Johnson, Christine Parseghian, John Paul Shen, Arvind Dasari, Kenna R. Shaw, Eduardo Vilar, Kanwal P. Raghav, Imad Shureiqi, Robert A. Wolff, Funda Meric-Bernstam, Dipen Maru, David G. Menter, Scott Kopetz, Shine Chang. Influence of pre-diagnosis obesity and post-diagnosis aspirin use on survival from stage IV colorectal cancer [abstract]. In: Proceedings of the AACR Special Conference on Colorectal Cancer; 2022 Oct 1-4; Portland, OR. Philadelphia (PA): AACR; Cancer Res 2022;82(23 Suppl_1):Abstract nr A023.

Antibiotic Exposure Does Not Impact Immune Checkpoint Blockade Response in MSI-H/dMMR Metastatic Colorectal Cancer: A Single-Center Experience

BACKGROUND

Immune checkpoint blockade (ICB) has improved outcomes for patients with microsatellite instability high (MSI-H)/deficient mismatch repair (dMMR) tumors. However, not all MSI-H/dMMR patients will exhibit the same ICB efficacy. Previous studies suggest that concomitant antibiotic use while receiving ICB may result in poorer outcomes. We aimed to evaluate this association in patients with MSI-H/dMMR metastatic colorectal cancer (mCRC).

MATERIALS AND METHODS

A single-site, retrospective review of 57 patients with MSI-H/dMMR mCRC that received ICB was completed. Data collected included patient demographics, ICB information, and antibiotic use. Antibiotic exposure was considered from 90 days prior to ICB through 6 weeks after initiation. Primary endpoint was overall response rate (ORR).

RESULTS

The majority of patients received pembrolizumab (27 [47%]) or nivolumab (17 [30%]) monotherapy as their ICB agent. Of the 57 patients, 19 (33.3%) had antibiotic exposure from 90 days prior to ICB initiation through 6 weeks after initiation with most (13 [68%]) having antibiotic use in the 30 days preceding ICB initiation. Similar ORRs were seen in both groups (P-value > .99). No difference was observed in OS (P-value .29) or PFS (P-value .36) between groups.

CONCLUSION

Our data show no association of lower response rates or survival in those MSI-H/dMMR patients with mCRC who receive antibiotics around the initiation of ICB. This information needs to be confirmed in a larger prospective cohort.

Association of Prediagnosis Obesity and Postdiagnosis Aspirin With Survival From Stage IV Colorectal Cancer

IMPORTANCE

The potential relationship between obesity and colorectal cancer (CRC) outcome is poorly understood in patients with late-stage disease. Increased body mass index may negate aspirin use for cancer prevention, but its role as a factor on the effectiveness of postdiagnosis aspirin use is unclear.

OBJECTIVE

To evaluate how prediagnosis obesity and postdiagnosis aspirin use may be associated with overall survival in patients with late-stage colorectal cancer.

DESIGN, SETTING, AND PARTICIPANTS

This cross-sectional study used self-reported data from patients with metastatic or treatment-refractory disease who consented to a clinical protocol at MD Anderson Cancer Center, a large US cancer treatment center. Patients were enrolled between 2010 and 2018 and followed up for mortality through July 2020. Analyses were conducted through March 2022.

EXPOSURES

Body mass index in the decade prior to initial diagnosis and regular aspirin use at survey completion.

MAIN OUTCOMES AND MEASURES

Overall survival was measured from stage IV diagnosis until death or last follow-up. Cox proportional hazards models were constructed to estimate associations of prediagnosis obesity and postdiagnosis aspirin use with overall survival.

RESULTS

Of 656 patients included in this analysis, 280 (42.7%) were women, 135 (20.6%) were diagnosed with CRC before age 45 years, 414 (63.1%) were diagnosed between ages 45 and 65 years, and 107 (16.3%) were diagnosed at 65 years or older; 105 patients (16.0%) were Black or Hispanic, and 501 (76.4%) were non-Hispanic White. Controlling for age, sex, race, stage at initial diagnosis, and weight change between prediagnosis and survey date, patients with obesity in the decade prior to CRC diagnosis had significantly higher likelihood of death (hazard ratio, 1.45; 95% CI, 1.11-1.91) compared with those with normal prediagnosis body mass index. Furthermore, only patients with normal prediagnosis body mass index experienced significant survival benefit with postdiagnosis aspirin use (hazard ratio, 0.59; 95% CI, 0.39-0.90).

CONCLUSIONS AND RELEVANCE

In this cross-sectional study, our findings suggest potentially differential tumor development in the long-term physiologic host environment of obesity. Confirmation and further evaluation are needed to determine whether prediagnosis body mass index may be used to estimate the benefit from postdiagnosis aspirin use.

Overall Survival in Phase 3 Clinical Trials and the Surveillance, Epidemiology, and End Results Database in Patients With Metastatic Colorectal Cancer, 1986-2016: A Systematic Review

IMPORTANCE

Phase 3 trials for patients with metastatic colorectal cancer (mCRC) have been conducted with varying designs and often with surrogate end points for overall survival (OS).

OBJECTIVES

To critically examine the factors associated with clinically relevant improvement in OS (defined as ≥2 months) in these trials and to evaluate their association with outcomes reflected in Surveillance, Epidemiology, and End Results (SEER) registry data.

EVIDENCE REVIEW

Medline, EMBASE, Cochrane, Web of Science, ClinicalTrials.gov, EU Clinical Trials Register, and the International Clinical Trials Registry Platform were searched for phase 3 trials of systemic therapy for patients with mCRC by decade (1986-1996, 1997-2006, and 2007-2016), excluding early or pilot studies, studies that did not involve an anticancer drug, studies on cancer screening and prevention, reports of pooled data from multiple trials, and studies with nonpharmaceutical approaches. The association of drug development with OS outside the clinical trial setting was evaluated using data from the SEER registry, including adult patients with a primary cancer site in the colon or rectum, including adenocarcinoma, mucinous adenocarcinoma, or signet ring cell carcinoma; a distant stage; and receipt of chemotherapy as first-line therapy. Kaplan-Meier curves and log-rank tests were used to assess OS.

FINDINGS

The literature search identified 150 phase III clinical trials with 77 494 total enrollments, and 67 126 patients with mCRC were identified from the SEER database. Significant increases in survival were noted over time, best reflected in the experimental arm of first-line therapy (OS increased by 5.7 months per 10 years; 95% CI, 4.7-6.6 months; progression-free survival increased by 1.4 months per 10 years; 95% CI, 0.7-2.1 months). Although 69 of 148 trials (46.6%) met their predefined primary end point (including 20 of 44 trials [45.5%] with OS as the primary end point), only 35 of 132 trials (26.5%) resulted in improvement in OS by 2 months or more (including 13 of 42 trials [31.0%] with OS as the primary end point). Multivariable logistic regression showed that third-line therapies or later (odds ratio, 0.57; 95% CI, 0.51-0.63) and funding by pharmaceutical companies (odds ratio, 0.57; 95% CI, 0.54-0.60) were less often associated with improvement in OS. Furthermore, there was a decrease in the novelty of targets and agents over time, with trials that evaluated regimens composed entirely of previously approved drugs for mCRC increasing from 28% to 50%. Data from the SEER database showed that median OS increased from 12 months (95% CI, 12-13 months) (1986-1996) to 21 months (95% CI, 21-22 months) (2007-2015) (P < .001), but the 5-year OS continued to be low at 12.2% in 2011.

CONCLUSIONS AND RELEVANCE

In this systematic review, OS for patients with mCRC appeared to improve significantly in trials, translating into meaningful benefits outside the clinical trial setting; however, these advances, although significant cumulatively, are largely incremental individually. These data should be a call to aim for larger gains from future trials with novel drugs, building on the increasing understanding of the biology of mCRC and sophisticated translational research tools.

Comprehensive Clinical and Molecular Characterization of KRAS G12C-Mutant Colorectal Cancer

PURPOSE

KRAS p.G12C mutations occur in approximately 3% of metastatic colorectal cancers (mCRC). Recently, two allosteric inhibitors of KRAS p.G12C have demonstrated activity in early phase clinical trials. There are no robust studies examining the behavior of this newly targetable population.

METHODS

We queried the MD Anderson Cancer Center data set for patients with colorectal cancer who harbored KRAS p.G12C mutations between January 2003 and September 2019. Patients were analyzed for clinical characteristics, overall survival (OS), and progression-free survival (PFS) and compared against KRAS nonG12C. Next, we analyzed several internal and external data sets to assess immune signatures, gene expression profiles, hypermethylation, co-occurring mutations, and proteomics.

RESULTS

Among the 4,632 patients with comprehensive molecular profiling, 134 (2.9%) were found to have KRAS p.G12C mutations. An additional 53 patients with single gene sequencing were included in clinical data but excluded from prevalence analysis allowing for 187 total patients. Sixty-five patients had de novo metastatic disease and received a median of two lines of chemotherapy without surgical intervention. For the first three lines of chemotherapy, the median PFS was 6.4 months (n = 65; 95% CI, 5.0 to 7.4 months), 3.9 months (n = 47; 95% CI, 2.9 to 5.9 months), and 3.0 months (n = 21; 95% CI, 2.0 to 3.4 months), respectively. KRAS p.G12C demonstrated higher rates of basal EGFR activation compared with KRAS nonG12C. When compared with an internal cohort of KRAS nonG12C, KRAS p.G12C patients had worse OS.

CONCLUSION

PFS is poor for patients with KRAS p.G12C metastatic colorectal cancer. OS was worse in KRAS p.G12C compared with KRAS nonG12C patients. Our data highlight the innate resistance to chemotherapy for KRAS p.G12C patients and serve as a historical comparator for future clinical trials.

Pilot Clinical Trial of Perioperative Durvalumab and Tremelimumab in the Treatment of Resectable Colorectal Cancer Liver Metastases

PURPOSE

Despite the prognostic importance of immune infiltrate in colorectal cancer, immunotherapy has demonstrated limited clinical activity in refractory metastatic proficient mismatch-repair (pMMR) colorectal cancer. This study explores combining anti-CTLA-4 and an anti-PD-L1 therapy in the preoperative management of resectable colorectal cancer liver metastases with the intent to improve immune responses in this disease setting.

PATIENTS AND METHODS

Patients with resectable colorectal cancer liver-only metastases received one dose of tremelimumab and durvalumab preoperatively followed by single-agent durvalumab postoperatively. Primary objectives were to determine feasibility and safety.

RESULTS

A total of 24 patients were enrolled between November 2016 and November 2019. Twenty-three patients received treatment [21 pMMR and 2 deficient mismatch-repair (dMMR)] and subsequently 17 (74%; 95% CI: 53%-88%) underwent surgical resection. Grade 3/4 treatment-related immune toxicity and postoperative grade 3/4 toxicity were seen in 5/23 (22%; 95% CI: 10%-44%) and 2/17 (12%; 95% CI: 2%-38%) patients. The median relapse-free survival (RFS) was 9.7 (95% CI: 8.1-17.8) months, and overall survival was 24.5 (95% CI: 16.5-28.4) months. Four patients demonstrated complete pathologic response, two dMMR patients and two POLE mutation patients. Pre- and post-tumor tissue analysis by flow cytometry, immunofluorescence, and RNA sequencing revealed similar levels of T-cell infiltration, but did demonstrate evidence of CD8⁺ and CD4⁺ activation posttreatment. An increase in B-cell transcriptome signature and B-cell density was present in posttreatment samples from patients with prolonged RFS.

CONCLUSIONS

This study demonstrates the safety of neoadjuvant combination tremelimumab and durvalumab prior to colorectal cancer liver resection. Evidence for T- and B-cell activation following this therapy was seen in pMMR metastatic colorectal cancer.

Identification of Actionable Fusions as an Anti-EGFR Resistance Mechanism Using a Circulating Tumor DNA Assay

PURPOSE

Gene fusions are established oncogenic drivers and emerging therapeutic targets in advanced colorectal cancer. This study aimed to detail the frequencies and clinicopathological features of gene fusions in colorectal cancer using a circulating tumor DNA assay.

METHODS

Circulating tumor DNA samples in patients with advanced colorectal cancer were analyzed at 4,581 unique time points using a validated plasma-based multigene assay that includes assessment of fusions in FGFR2, FGFR3, RET, ALK, NTRK1, and ROS1. Associations between fusions and clinicopathological features were measured using Fisher's exact test. Relative frequencies of genomic alterations were compared between fusion-present and fusion-absent cases using an unpaired t test.

RESULTS

Forty-four unique fusions were identified in 40 (1.1%) of the 3,808 patients with circulating tumor DNA detected: RET (n = 6; 36% of all fusions detected), FGFR3 (n = 2; 27%), ALK (n = 10, 23%), NTRK1 (n = 3; 7%), ROS1 (n = 2; 5%), and FGFR2 (n = 1; 2%). Relative to nonfusion variants detected, fusions were more likely to be subclonal (odds ratio, 8.2; 95% CI, 2.94 to 23.00; P < .001). Mutations associated with a previously reported anti-epidermal growth factor receptor (anti-EGFR) therapy resistance signature (subclonal RAS and EGFR mutations) were found with fusions in FGFR3 (10 of 12 patients), RET (nine of 16 patients), and ALK (seven of 10 patients). For the 27 patients with available clinical histories, 21 (78%) had EGFR monoclonal antibody treatment before fusion detection.

CONCLUSION

Diverse and potentially actionable fusions can be detected using a circulating tumor DNA assay in patients with advanced colorectal cancer. Distribution of coexisting subclonal mutations in EGFR, KRAS, and NRAS in a subset of the patients with fusion-present colorectal cancer suggests that these fusions may arise as a novel mechanism of resistance to anti-EGFR therapies in patients with metastatic colorectal cancer.

Circulating DNA Demonstrates Convergent Evolution and Common Resistance Mechanisms during Treatment of Colorectal Cancer

Purpose: Liquid biopsies allow the tracking of clonal dynamics and detection of mutations during treatment.Experimental Design: We evaluated under blinded conditions the ability of cell-free DNA (cfDNA) to detect RAS/BRAF mutations in the plasma of 42 metastatic colorectal cancer patients treated on a phase Ib/II trial of FOLFOX and dasatinib, with or without cetuximab.Results: Prior to treatment, sequencing of archival tissue detected mutations in 25 of 42 patients (60%), while the cfDNA assay detected mutations in 37 of 42 patients (88%). Our cfDNA assay detected mutations with allele frequencies as low as 0.01%. After exposure to treatment, 41 of 42 patients (98%) had a cfDNA-detected RAS/BRAF mutation. Of 21 patients followed with serial measurements who were RAS/BRAF mutant at baseline, 11 (52%) showed additional point mutation following treatment and 3 (14%) no longer had detectable levels of another mutant allele. Of RAS/BRAF wild-type tumors at baseline, 4 of 5 (80%) showed additional point mutations. cfDNA quantitative measurements from this study closely mirrored changes in CEA and CT scan results, highlighting the importance of obtaining quantitative data beyond the mere presence of a mutation.Conclusions: Our findings demonstrate the development of new RAS/BRAF mutations in patients regardless of whether they had preexisting mutations in the pathway, demonstrating a convergent evolutionary pattern. Clin Cancer Res; 23(16); 4578-91. ©2017 AACR.

Abstract 2924: Circulating DNA demonstrates convergent evolution and common resistance mechanisms during treatment of colorectal cancer

Malignant tumors shed cell free DNA into the blood stream. Analyzing this new biological source may have important implications in a shift towards personalized medicine for diagnosing and/or monitoring malignancies. We recently showed the first clinical validation and clinical utility of circulating DNA (cfDNA) analysis in oncology by testing RAS/BRAF hotspot mutations in plasma from metastatic colorectal cancer patients (mCRC) (Nat Med. 2014 Apr;20(4):430-5). In addition, liquid biopsies allow the tracking of clonal dynamics and detection of mutations during treatment. We evaluated under blinded conditions the ability of cfDNA to detect RAS/BRAF mutations in the plasma of 42 mCRC patients treated on a phase Ib/II trial of FOLFOX and dasatnib, with or without cetuximab. Prior to treatment, sequencing of archival tissue detected mutations in 25/42 patients (60%), while the cfDNA assay detected mutations in 37/42 patients (88%). Our cfDNA assay was able to detect mutations with allele frequencies as low as 0.01%. After exposure to treatment, 41/42 patients (98%) had a cfDNA detected RAS/BRAF mutation. Of 22 patients followed with serial measurements who were RAS/BRAF mutant at baseline, 11 (50%) developed a second mutation following treatment and 3 (14%) no longer had detectable levels of another mutant allele. Of RAS/BRAF wild type tumors at baseline, 4/5 (80%) developed new mutations. Patients may harbor mutations at very low frequency down to 0.01% before initiation or during treatment revealing the need of a high sensitive technique to detect mutant subclones. cfDNA quantitative measurements from this study closely mirrored changes in CEA and CT scan results, highlighting the importance of obtaining quantitative data beyond the mere presence of a mutation. Combined qualitative and quantitative cfDNA analysis allows tracking acquired resistance by studying the real-time clonal evolution of the tumor and might help physicians to adjust patient treatment. Our findings demonstrate the development of new RAS/BRAF mutations in patients regardless of whether they had pre-existing mutations in the pathway, demonstrating a convergent evolutionary pattern.

Note: This abstract was not presented at the meeting.

Citation Format: Alain R. Thierry, Brice Pastor, Zhi-Qin Camilla Jiang, anastasia Katsiampoura, Christine Parseghian, Jonathan Loree, Michael J. Overman, Cynthia Sanchez, Safia El Messaoudi, Marc Ychou, Scott Kopetz. Circulating DNA demonstrates convergent evolution and common resistance mechanisms during treatment of colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2924. doi:10.1158/1538-7445.AM2017-2924