3525 Background: FOLFOX4 has shown superiority over LV5FU2 and IFL in first line therapy. Limiting toxicities are neutropenia mainly due to 5FU bolus and cumulative sensory neurotoxicity which imposes to stop oxaliplatin (ox). OPTIMOX is a phase III study in pts with conventional inclusion criteria (526 pts), and two exploratory studies in pts not included in previous studies (37 pts > 75 yrs, 63 pts Alk Ph > 3xUNV) of a new strategy with ox stop and go: FOLFOX7 (high-dose ox and 5FU infusion, 6 cy) followed by 12 cy simplified (s) LV5FU2 and later FOLFOX7 reintroduction. Methods : 526 pts ≤ 75 yrs and/or Alk Ph ≤ 3xUNL were randomized Arm A FOLFOX4 (Ox 85mg/m2 d1, LV 200mg/m2, 5FU bolus 400mg/m2 and 22h 600mg/m2 d1–2, q2w) or Arm B FOLFOX7 x 6 cy (ox 130mg/m2 d1, LV 400mg/m2, 5FU 46h 2.4g/m2, q2w) followed by sLV5FU2 x 12 cy (LV 400mg/m2, 5FU bolus 400mg/m2 d1 and 46-h infusion 2.4g/m2, q2w) then FOLFOX7 reintroduction. Results : Arm A, 262 pts: M/F 58/42%, PS 0/1–2 55/45%, median age 63 yrs; Arm B, 264 pts: M/F 62/38%, PS 0/1–2 56/44%, median age 63 yrs. 3514 cy (2938 with ox, median DI 41.9mg/m2/wk) were administered in arm A and 4107 cy (2076 with ox, median DI 62.2mg/m2/wk) in arm B. Grade 3–4 toxicity (pts %) was in arm A/B : neutrophils 33.2/21.9, platelets 3.1/10.6, nausea 5.7/9.4, mucositis 3.1/6.5, diarrhea 11.1/11.8, neuro 18.7/13.3, maximal 54.6/49.2. RR was 58.8% in arm A and 59.5% in arm B. 28 pts arm A and 26 pts arm B had complete resection of metastasis. In arm A and B, median PFS were 9.2 and 9.0 months (P=0.47), median OS were 20.7 and 21.4 months (P=0.75), respectively. The primary endpoint is time of disease control (TDC=PFS first FOLFOX+PFS reintroduction if PR or SD), median TDC was 9.9 arm A and 11.3 months arm B (P=0.61). Ox was reintroduced in 8.4% pts arm A and 42% arm B. Reintroduction achieved 11.6% RR, 33.9% SD. Post study, in arm A 17.6% pts received ox-based and 58.3% irinotecan-based regimen, in arm B 13.3% received ox-based and 58.3% irinotecan-based regimens. Conclusions : The optimox stop and go strategy is a convenient alternative to FOLFOX4 in first-line therapy. Further studies will use a lower oxaliplatin dose-intensity to improve the reintroducction rate and evaluate lack of sLV5FU2 maintenance. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Sanofi-Synthelabo Sanofi-Synthelabo