Newly detected KRAS and/or EGFR mutations in plasma ctDNA from patients refractory to anti-EGFR treatment appear to derive from rare, pre-existing clones in the primary tumors. These rare clones were associated with shorter PFS in patients receiving anti-EGFR treatment. Multiple simultaneous mutations in KRAS and EGFR in the ctDNA and the decline in allele frequency after discontinuation of anti-EGFR therapy in a subset of patients suggest that several resistance mechanisms can co-exist and that relative clonal burdens may change over time. Monitoring treatment-induced genetic alterations by sequencing ctDNA could identify biomarkers for treatment screening in anti-EGFR-refractory patients.

Background: Colorectal cancer (CRC) has been shown to acquire RAS and EGFR ectodomain mutations as mechanisms of resistance to epidermal growth factor receptor (EGFR) inhibition (anti-EGFR). After anti-EGFR withdrawal, RAS and EGFR mutant clones lack a growth advantage relative to other clones and decay; however, the kinetics of decay remain unclear. We sought to determine the kinetics of acquired RAS/EGFR mutations after discontinuation of anti-EGFR therapy.Patients and methods: We present the post-progression circulating tumor DNA (ctDNA) profiles of 135 patients with RAS/ BRAF wild-type metastatic CRC treated with anti-EGFR who acquired RAS and/or EGFR mutations during therapy. Our validation cohort consisted of an external dataset of 73 patients with a ctDNA profile suggestive of prior anti-EGFR exposure and serial sampling. A separate retrospective cohort of 80 patients was used to evaluate overall response rate and progression free survival during re-challenge therapies.Results: Our analysis showed that RAS and EGFR relative mutant allele frequency decays exponentially (r 2 ¼0.93 for RAS; r 2 ¼0.94 for EGFR) with a cumulative half-life of 4.4 months. We validated our findings using an external dataset of 73 patients with a ctDNA profile suggestive of prior anti-EGFR exposure and serial sampling, confirming exponential decay with an estimated half-life of 4.3 months. A separate retrospective cohort of 80 patients showed that patients had a higher overall response rate during re-challenge therapies after increasing time intervals, as predicted by our model. Conclusion:These results provide scientific support for anti-EGFR re-challenge and guide the optimal timing of re-challenge initiation.

In vitro, EGFR inhibition, combined with the BRAF inhibitor vemurafenib, causes synergistic cytotoxicity for BRAFV600E metastatic colorectal cancer (mCRC), further augmented by irinotecan. The safety and efficacy of vemurafenib, irinotecan, and cetuximab in BRAF-mutated malignancies are not defined. In this 3+3 phase I study, patients with BRAFV600E advanced solid cancers received cetuximab and irinotecan with escalating doses of vemurafenib. Nineteen patients (18 with mCRC, 1 with appendiceal cancer) were enrolled. Three patients experienced dose-limiting toxicities. The maximum tolerated dose of vemurafenib was 960 mg twice daily. Six of 17 evaluable patients (35%) achieved a radiographic response by RECIST 1.1 criteria, consistent with in vivo models demonstrating tumor regressions with the triplet regimen. Median progression-free survival was 7.7 months. BRAFV600E cfDNA trends correlated with radiographic changes, and acquired mutations from cfDNA in genes reactivating MAPK signaling were observed at progression.

Background:Patients with type II diabetes mellitus (DM) have an increased risk of adenomatous colorectal (CRC) polyps and CRC cancer. The use of the anti-hyperglycemic agent metformin is associated with a reduced incidence of cancer-related deaths.Methods:We retrospectively evaluated the medical records of 4758 patients seen at a single institution and determined that 424 patients were identified by their physicians as having type II DM and CRC cancer. Data were subsequently acquired determining the subject's age, body mass index (BMI), and disease date of diagnosis, stage, site of cancer, treatment, and survival.Results:Patients with type II DM and CRC cancer treated with metformin as one of their diabetic medications had a survival of 76.9 months (95% CI=61.4–102.4) as compared with 56.9 months in those patients not treated with metformin (95% CI=44.8–68.8), P=0.048. By using a multivariable Cox regression model adjusted for age, sex, race, BMI, and initial stage of disease, we demonstrated that type II diabetic patients treated with metformin had a 30% improvement in overall survival (OS) when compared with diabetic patients treated with other diabetic agents.Conclusion:Colorectal cancer patients with DM treated with metformin as part of their diabetic therapy appear to have a superior OS.

Background BRAF mutations occur in 5–10% of metastatic colorectal cancers and are biomarkers associated with a poor prognosis. However, the outcomes with standard chemotherapy over sequential lines of therapy in a large cohort of patients with BRAF-mutant tumors have not been described. Methods We searched the MD Anderson Cancer Center databases for patients with colorectal cancer patients and identified BRAF mutations between December 2003 and May 2012. Patients were analyzed for clinical characteristics, progression-free survival (PFS), overall survival (OS), and chemotherapeutic agents used. Survival was estimated according to the Kaplan-Meier method. Results Among the 1567 patients tested for BRAF mutations at our institution, 127 (8.1%) had tumors with BRAF mutations. The 71 patients who presented with metastatic disease received a median of 2 lines of chemotherapy. For the first three lines of chemotherapy, median progression-free survivals were 6.3 months (n=69 patients, 95% confidence interval (CI) of 4.9–7.7 months), 2.5 months (n=58, 95% CI of 1.8–3.0 months), and 2.6 months (n=31, 95% CI of 1.0–4.2 months), respectively. Median PFS was not affected by the backbone chemotherapeutic agent in the first-line setting, whether oxaliplatin-based or irinotecan-based (6.4 months vs. 5.4 months, respectively, p-value = 0.99). Conclusions Progression-free survival is expectedly poor for patients with BRAF-mutated metastatic colorectal cancer. Despite the ascertainment bias present (with testing preferentially performed in patients suitable for clinical trials in refractory disease), these data provide historic controls suitable for future study design and support the idea that novel therapeutic options are essential in this population.