Maintenance treatment with cetuximab versus observation in RAS wild-type metastatic colorectal cancer: Results of the randomized phase II PRODIGE 28-time UNICANCER study.

15 Background: Compared to observation, maintenance therapy with a fluoropyrimidine +/- bevacizumab showed significant improvement in progression-free survival (PFS) but not in overall survival (OS) in patients with unresectable metastatic colorectal cancer (mCRC) and disease control after first-line doublet chemotherapy (CT) +/- bevacizumab. Few studies are available on the role of maintenance therapy after induction anti-EGFR-based CT, and the benefit from anti-EGFR maintenance monotherapy during CT-free intervals (CFI) in patients with RAS wild-type (wt) mCRC. Methods: RAS wt unresectable mCRC patients with controlled disease after FOLFIRI + cetuximab (8 cycles) were randomized (1:1) to receive maintenance with bi-weekly cetuximab alone (arm A) or observation (arm B) until disease progression (PD)/unacceptable toxicity/death. Randomization was stratified according to tumor response, center, baseline Köhne Score, CEA and platelet count. In case of tumor progression during the CFI, FOLFIRI + cetuximab was to be reintroduced for 8 cycles, followed by a new CFI. Tumor response was assessed per RECIST1.1 every 8 weeks. The primary objective of this multicenter non-comparative randomized phase II trial was 6-month PFS rate after initiation of maintenance therapy. A total of 134 randomized and evaluable patients (67 per arm) were required (Fleming’s one-step design, one-sided α=5%, β=20%, H0: 40%; H1: 55%). Secondary endpoints were overall response rate (ORR), time to strategy failure, PFS, OS, safety, quality of life, circulating tumor cells and circulating tumor DNA detection and dynamic changes during treatment. Results: From January 2014 to April 2019, 214 patients were included and 139 randomized (67 arm A/72 arm B) in 35 centers. Baseline characteristics were: males, 67%/69%; median age, 64/68 years; ECOG PS 0, 54%/46%; previous adjuvant therapy, 25%/14%; single metastatic site, 58%/47%; right-sided primary, 24%/18%. The ORR in the overall and the randomized population was 55% and 72%, respectively. The median follow-up was 30 months. The 6-month PFS rate after initiation of maintenance therapy was 30% 95%CI[19; 42] in the maintenance arm, and 6% 95%CI[2;14] in the observation arm, with a median PFS of 5.3 95%CI[3.7;6.5] and 2.0 95%CI[1.8;2.8] months, respectively. Any grade treatment-related toxicity, including skin rash (40%/4%), diarrhea (33%/8%), and hypomagnesemia (46%/10%) was more frequent in arm A. Conclusions: Based on the study hypothesis, the cetuximab maintenance arm did not meet the primary objective. However, the clinically meaningful difference in PFS without any overlap in the confidence intervals between the two arms warrants further investigation. Clinical trial information: NCT02404935.