Definition of oxaliplatin sensitivity in patients with advanced colorectal cancer previously treated with oxaliplatin-based therapy

4024 Background: Oxaliplatin combined with fluoropyrimidines is standard adjuvant therapy in stage III colon cancer and first-line therapy in stage IV colorectal cancer. Oxaliplatin can be reintroduced either at relapse, or after maintenance or after chemotherapy holidays. In this study we defined the sensitivity to oxaliplatin reintroduction based on the oxaliplatin-free interval. Methods: Stage IV pts entered in the OPTIMOX1 and 2 studies (FOLFOX4, FOLFOX7 followed by maintenance without oxaliplatin or chemotherapy holidays) and pts having relapsed after metastases surgery and neoadjuvant or adjuvant FOLFOX for resectable stage IV were eligible if they were rechallenged with FOLFOX. Endpoints were: survival from reintroduction according to interval between the last cycle of oxaliplatin first-line and reintroduction, survival and response at reintroduction according to first FOLFOX response and PFS. Results: 330 pts were included: male 60%, colon/rectum/both 62%/35%/2%, resectable/unresectable: 14%/86%, PS 0–1 / >1: 90%/10%, sites 1/>1: 57%/43%. 23 pts had adjuvant and 22 pts had neoadjuvant chemotherapy. 58 pts (18%) had FOLFOX reintroduction before progression. PFS/OS from reintroduction according to induction FOLFOX response were 8.7/19.5 mths if CR, 4.6/15.2 mths if PR, and 3.2/9.7 mths if SD (P=.0019/.01). PFS/OS from reintroduction according to induction FOLFOX PFS were 2.9/9.3 mths if PFS<6 mths, 4.6/14.7 mths if PFS 6–12 mths and 8.5/23.7 if PFS=12 mths. Table shows results according to intervals. There was no difference between 0–3 and 3–6 mths or 6–9 and 9–12 mths intervals. Conclusions: A prolonged interval between two FOLFOX therapies or a prolonged PFS at first-line FOLFOX predict the efficacy of oxaliplatin reintroduction. The interval between two FOLFOX therapies does not identify a completely refractory population. Resistance (PD rate) is divided by two at each 6 month intervals. [Table: see text] No significant financial relationships to disclose.