Right-sided colorectal cancer (RC): Response to first-line chemotherapy in FIRE-3 (AIO KRK-0306) with focus on early tumor shrinkage (ETS) and depth of response (DpR).
3586 Background: Recent evidence suggests that benefit from anti-EGFR treatment is restricted to RAS wild-type left-sided colorectal cancer (LC) (Holch JW et al. Eur J Cancer 2017). However, these results are preliminary. We therefore investigated patients with RC enrolled in the FIRE-3 trial, which evaluated the efficacy of first-line FOLFIRI plus either cetuximab (cet) or bevacizumab (bev) in RAS wildtype mCRC. New metrics of tumor dynamics were used to characterize the patients. Methods: The splenic flexure was used to differentiate LC from RC. Survival analysis was done using Kaplan-Meier estimation and differences were expressed using Log-Rank test, hazard ratios (HR) and corresponding 95% confidence intervals. Central independent radiological data was used to calculate early tumor shrinkage ≥20% (ETS) and depth of response (DpR). Results: In total, 330 patients were assessable for central radiological evaluation. In patients with LC (n = 257), treatment with FOLFIRI + cet led to longer overall survival (OS) compared to FOLFIRI + bev (HR = 0.68, p = 0.016). In patients with RC (n = 68), OS was comparable between treatment arms (HR = 1.11, p = 0.715). In patients with RC and ETS < 20%, OS was inferior in patients treated with FOLFIRI + cet. In patients who reached ETS ≥20%, a comparable OS was evident between treatment arms (for further details of efficacy in patients with RC see table). Conclusions: Patients with RC do not represent a uniform population. ETS ≥20% defines a subgroup of patients where comparable treatment efficacy was observed with regard to OS, ORR and DpR by addition of cetuximab vs. bevacizumab to FOLFIRI. [Table: see text]