Early Tumor Shrinkage and Depth of Response as Predictors of Favorable Treatment Outcomes in Patients with Metastatic Colorectal Cancer Treated with FOLFOX Plus Cetuximab (JACCRO CC-05).

Background: Retrospective studies have found that early tumor shrinkage (ETS) and depth of response (DpR) are associated with favorable outcomes in patients with metastatic colorectal cancer (mCRC); however, few prospective studies have evaluated ETS and DpR.

Patients And Methods: We performed a phase II study of FOLFOX plus cetuximab as first-line treatment in Japanese patients with KRAS wild-type mCRC. The primary endpoint was response rate (RR), and secondary endpoints included progression-free survival (PFS), overall survival (OS), chronological tumor shrinkage (evaluated every 8 weeks), and safety. The association of ETS and DpR with survival time was analyzed using Spearman's rank correlation coefficient.

Results: In 54 participants, the RR, median PFS, and OS were 66.7 % (95 % CI, 53.4-77.8 %), 11.1 months, and 33.9 months, respectively. There was no unexpected toxicity. Forty (80 %) of 50 assessable patients had ETS, which was associated with prolonged PFS and OS (11.3 vs. 3.7 months, HR 0.26, p = 0.0003; 42.8 vs. 9.0 months, HR 0.40, p = 0.0279, respectively). Median DpR was 56.3 %. The DpR correlated with OS (r  = 0.314, p = 0.027) as well as post-progression survival (PPS) (r  = 0.366, p = 0.017). Interestingly, DpR was moderately associated with OS and PPS (r  = 0.587, r  = 0.570, respectively) in patients harboring tumors with larger target lesions, but was not associated with OS or PPS in patients with smaller target lesions. FOLFOX plus cetuximab was active as a first-line treatment for Japanese mCRC patients, with no unexpected toxicities.

Conclusions: Our prospective evaluation of chronological tumor shrinkage showed that ETS and DpR correlate with outcomes in patients with KRAS wild-type mCRC who receive cetuximab-based chemotherapy (UMIN000004197).