AGITG MONARCC: A Randomized Phase 2 Study of Panitumumab Monotherapy and Panitumumab Plus 5-Fluorouracil as First-Line Therapy for Older Patients With RAS and BRAF Wild Type Metastatic Colorectal Cancer. A Study by the Australasian Gastro-Intestinal Trials Group (AGITG).

Background: Panitumumab (pan) plus chemotherapy is a preferred first-line therapy for unresectable RAS and BRAF wild type metastatic colorectal cancer (mCRC). Older patients may not be suitable for combination regimens. We investigated 2 lower intensity pan-containing regimens.

Methods: Prospective, noncomparative, randomized (1:1) phase 2 study of pan alone (Arm A) or pan plus FU (Arm B). Previously untreated mCRC were ≥70 years; RAS/BRAF wild type.

Primary Endpoint: 6-month progression-free survival (PFS). Secondary endpoints included: overall survival (OS), response rate (RR), feasibility of geriatric assessments and overall treatment utility (OTU)-a composite measure based on radiological response, clinical progress, toxicity and patient-reported treatment worth. Planned sample size was 40 patients per arm.

Results: 36 patients (Arm A n = 19, Arm B n = 17) were randomized between June 2018 and June 2021. Median age was 79 and 80 years respectively. 6-month PFS 63% (95% CI 38%-80%) arm A 82% (95%CI 55%-94%) Arm B. Median OS 21 months Arm A (95%CI 13-31) 28 (95%CI 14-39) months Arm B. RR 47% and 65% Arms A and B respectively. Baseline comprehensive geriatric assessments were completed in >80% of patients. At week 16, OTU was categorized as good in 92% (Arm A) and 90% (Arm B). No unexpected adverse events were seen.

Conclusions: Six-month PFS in both arms was consistent with that achieved with FU/bev, whilst the rate was numerically higher for Arm B. Baseline comprehensive geriatric assessments were feasible and OTU was high. Both treatment arms might be suitable in appropriately selected patients.