Targeting EGFR and RAS/RAF Signaling in the Treatment of Metastatic Colorectal Cancer: From Current Treatment Strategies to Future Perspectives

The epidermal growth factor receptor (EGFR) and RAS/RAF signaling pathway plays pivotal roles in tumor progression via proliferation, survival, invasion, and immune evasion. Two anti-EGFR monoclonal antibodies, cetuximab and panitumumab, have become essential components in the treatment of patients with metastatic colorectal cancer (mCRC). Treatment with these anti-EGFR antibodies has shown definite benefits when administered in all treatment lines and is strongly recommended as the preferred regimen to prolong survival, especially when administered in the first- and third-lines. Recent efforts have revealed not only mechanisms responsible for resistance to anti-EGFR antibodies, including expanded RAS mutations as a negative predictive biomarker, but also the possibility of continuing anti-EGFR antibody treatment in combination with chemotherapy. Furthermore, the challenges associated with the pharmaceutical development of treatments for patients with mutant-type BRAF mCRC are ongoing. In this review, we provide an overview of the EGFR and RAS/RAF signaling pathway and antitumor activity, focusing on practical aspects such as established treatments including patient selection, treatment strategies, and future perspectives for drug development targeting the EGFR and RAS/RAF signaling pathway.

Phase I study of the anti-heparin-binding epidermal growth factor-like growth factor antibody U3-1565 with cetuximab in patients with cetuximab- or panitumumab-resistant metastatic colorectal cancer

KRAS wild-type colorectal cancers initially responsive to anti-endothelial growth factor receptor (EGFR) antibodies [cetuximab (Cetu)/panitumumab (Pani)] develop acquired resistance. Overexpression of EGFR ligands such as heparin-binding EGF-like growth factor (HB-EGF) may be one resistance mechanism. This phase I study of U3-1565, anti-HB-EGF antibody, and Cetu combination therapy enrolled patients with KRAS wild-type metastatic colorectal cancer who had received two ≤ regimens with fluoropyrimidine, oxaliplatin, irinotecan, and Cetu/Pani and had disease progression on Cetu/Pani. Recommended dose (RD) was determined in the 1st stage, followed by evaluation of efficacy at the RD level in the 2nd-stage. Cetu was given at a loading dose of 400 mg/m² followed by weekly infusions of 250 mg/m² in levels 1 and 0. U3-1565 was administered at a loading dose of 24 mg/m² followed by biweekly infusions of 16 mg/m² in level 1 and 16-12 mg/m² in level 0. Twenty-two patients were enrolled. No dose-limiting toxicities were observed among three patients in level 1 in the first stage, which was determined as RD. Grade 3 or higher adverse events occurred in 59.1%; those in ≥5% of patients were anemia, γ-GTP elevation, and acneiform rash. Overall response rate was 0.0% [95% confidence interval (CI): 0.0%-15.4%] and disease control was achieved in 17 patients (77.3%, 95% CI: 54.6%-92.2%). Median progression-free survival time was 85.0 days (95% CI: 54.0-91.0) and median survival time was 196 days (95% CI: 113.0-306.0). RD was determined as level 1. The efficacy of this combination therapy after progression on Cetu/Pani was negligible. Trial Registration: UMIN000013006.

Cetuximab retreatment in patients with metastatic colorectal cancer who exhibited a clinical benefit in response to prior cetuximab: A retrospective study

Clinical benefits of cetuximab retreatment in patients with metastatic colorectal (mCRC) have been reported. In the present study, the effect of cetuximab retreatment on predictive markers was investigated by evaluating the clinical benefit of initial cetuximab treatment prior to cetuximab retreatment. Between November 2012 and March 2017, 14 patients with KRAS proto-oncogene GTPase exon 2 wild-type mCRC who exhibited a clinical benefit (confirmed stable disease for at least 6 months or a clinical response) to an initial cetuximab-based regimen, who received multiple lines of chemotherapy following disease progression and ultimately received a second cetuximab and irinotecan regimen, were retrospectively analyzed. For retreatment, patients received bi-weekly irinotecan (120-150 mg/m²) combined with cetuximab (400 mg/m² as an initial dose, followed by 250 mg/m², weekly). The median age of the 14 patients (11 males, 3 females) was 68 years (32-77). The median progression-free survival (PFS) following prior cetuximab-based therapy was 6.6 months (range, 4.1-18.4). Initial cetuximab treatment was administered as a first-line treatment in 11 patients, a second-line treatment in 1 patient and a third-line treatment in 2 patients. The median interval time between the last cycle of initial cetuximab-based therapy and the first cycle of cetuximab retreatment was 13.1 months (range, 6.0-37.1). The objective response rate of cetuximab retreatment was 21.4% and the median PFS was 4.4 months (95% confidence interval, 1.4-5.6). The Spearman's correlation coefficient for the PFS following retreatment and duration of initial cetuximab-based regimens demonstrated a more marked correlation compared with that between the PFS following retreatment and the interval time between the two regimens (r=0.45, P=0.11 vs. r=0.08, P=0.79). Cetuximab retreatment may provide clinical benefit to patients with mCRC who were good responders with longer periods of initial cetuximab-based therapy.