Abstract 415P
Background
In patients with RAS wild-type (wt) metastatic colorectal cancer (mCRC) receiving first-line treatment with cetuximab (CET) in combination with chemotherapy, the noninferiority of the off-label schedule of CET 500 mg/m2 every 2 weeks (q2w) compared with the approved schedule of CET at an initial dose of 400 mg/m2 followed by weekly doses of 250 mg/m2 (q1w) was shown in a pooled analysis of patient-level data from 2 noninterventional studies (EREBUS, ERBITAG) and 3 clinical trials (CEBIFOX, CECOG/CORE 1.2.002, APEC). In terms of overall survival (OS), consistent findings were shown in patients with left- and right-sided primary tumors (Kasper S, et al. Ann Oncol. 2021;32(Supp X) to be published for WCGC 2021). We present the results in terms of overall response rate (ORR), disease control rate (DCR), resection rate of lung/liver metastases, and serious adverse events (SAEs) by primary tumor location (PTL).
Methods
The main analyses were repeated in subgroups of patients with left- and right-sided primary tumors. Outcomes were assessed via logistic regression models after inverse probability of treatment weighting (IPTW) using a propensity score considering the same variables as in the main analysis, to account for differences in baseline characteristics between treatment schedules.
Results
A total of 830 (79%) and 227 (21%) patients presented with left- and right-sided PTLs, respectively. After IPTW, baseline confounders were balanced. No major differences were seen between the 2 administration schedules in ORR, DCR, resection rates, or SAEs (Table) in either PTL subgroup. Table: 415P
| Side of primary tumor location | After IPTW | |||
| Rate % (95% CI) | Odds ratio (95% CI) | |||
| q1w n=830 | q2w n=227 | q2w vs q1w | ||
| ORR | Left | 62.1 (57.65-66.51) | 69.4 (64.64-74.23) | 1.387 (1.036-1.857) |
| Right | 42.3 (33.63-50.92) | 40.5 (30.70-50.22) | 0.928 (0.545-1.581) | |
| DCR | Left | 75.6 (71.72-79.55) | 81.4 (77.32-85.44) | 1.408 (1.003-1.976) |
| Right | 62.0 (53.40-70.51) | 61.9 (51.97-71.85) | 0.998 (0.579-1.720) | |
| Resection rate of lung/liver metastases | Left | 19.5 (15.68-23.39) | 23.7 (19.04-28.39) | 1.280 (0.899-1.824) |
| Right | 12.5 (5.40-19.49) | 13.0 (5.44-20.46) | 1.047 (0.416-2.634) | |
| SAEs | Left | 26.8 (22.80-30.85) | 30.3 (25.51-35.09) | 1.186 (0.876-1.607) |
| Right | 32.4 (24.12-40.61) | 33.7 (24.18-43.14) | 1.061 (0.606-1.857) |
Conclusions
These subgroup analyses support the consistent findings observed for OS in patients with RAS wt mCRC with left- and right-sided PTLs treated with first-line q2w vs q1w CET in combination with chemotherapy. No significant difference was shown in terms of frequency of any SAEs.
Clinical trial identification
EMR062202_0110; 07 February 2019.
Editorial acknowledgement
Editorial assistance was provided by Michelle Olsher, PhD of ClinicalThinking, Inc.
Legal entity responsible for the study
Merck KGaA, Darmstadt, Germany.
Funding
Merck KGaA, Darmstadt, Germany.
Disclosure
S. Kasper: Financial Interests, Personal and Institutional, Other, Honoraria: Merck; Roche; Amgen; Lilly; Financial Interests, Personal, Other, Honoraria: Sanofi-Aventis; Servier; Financial Interests, Personal, Other, Travel/accommodation expenses: Merck; Amgen; Amgen; Roche; Sanofi-Aventis; Servier; Lilly; BMS; Financial Interests, Personal and Institutional, Research Grant: Roche; Merck; Lilly; BMS; Financial Interests, Personal, Advisory Role: Merck; Amgen; Roche; Sanofi-Aventis; Servier; Lilly; BMS; MSD. C. Foch: Financial Interests, Personal, Full or part-time Employment: Merck KGaA. F. Lamy: Financial Interests, Personal, Full or part-time Employment, This author was a full-time employee of Merck KGaA at the time the study work was done: Merck KGaA. R. Esser: Financial Interests, Personal, Full or part-time Employment, This author was a full-time employee of Merck KGaA at the time the study work was done: Merck KGaA. M. Batech: Financial Interests, Personal, Full or part-time Employment, This author was a full-time employee of Merck KGaA at the time the study work was done: Merck KGaA. C.M.J. Wong: Financial Interests, Personal, Full or part-time Employment, This author is an employee of Cytel which Merck KGaA has engaged to perform analytical services.: Cytel. A. Zhang: Financial Interests, Personal, Full or part-time Employment, Merck Serono Co., Ltd., China is a business of Merck KGaA, Darmstadt, Germany: Merck Serono Co., Ltd., China. T. Brodowicz: Financial Interests, Personal, Other, Lecture fee: Roche; Amgen; Bayer; Novartis; PharmaMar; Eisai; Lilly; Financial Interests, Personal, Advisory Board: Amgen; Bayer; Novartis; PharmaMar; Eisai; Lilly. C. Zielinski: Financial Interests, Personal, Other, Consultancy: Roche; Novartis; BMS; MSD; Imugene; ARIAD; Pfizer; Merrimack; Merck KGaA; FibroGen; AstraZeneca; Tesaro; Gilead; Servier; Shire; Lilly; Athenex; Financial Interests, Personal, Other, Speaker's honoraria: Roche; Novartis; BMS; MSD; Imugene; ARIAD; Pfizer; Merrimack; Merck KGaA; FibroGen; AstraZeneca; Tesaro; Gilead; Servier; Shire; Lilly; Athenex; All other authors have declared no conflicts of interest.