Associations between deepness of response and clinical outcomes among Japanese patients with metastatic colorectal cancer treated with second-line FOLFIRI plus cetuximab

Background: In the FIRE-3 trial, overall survival (OS) was significantly longer in patients treated with FOLFIRI plus cetuximab (C-mab) than in those treated with FOLFIRI plus bevacizumab (Bev), but progression-free survival (PFS) was not significantly different. This may be associated with the deepness of response (DpR) in patients treated with FOLFIRI plus C-mab. We aimed to evaluate the relationship between clinical outcome and DpR in metastatic colorectal cancer (mCRC) patients treated with second-line FOLFIRI plus C-mab. Methods: A total of 112 patients with histopathologically confirmed mCRC treated with second-line FOLFIRI in combination with C-mab (N= 42) or Bev (N= 70) were retrospectively enrolled between October 2008 and June 2013. The relationship between DpR and clinical outcome in patients treated with FOLFIRI plus C-mab or Bev was determined. Results: Forty-two patients treated with FOLFIRI plus C-mab had a mean DpR of 6.1% (interquartile range: -13.7%, 20.8%) and a minimum DpR of -62.7%. On the other hand, 70 patients treated with FOLFIRI plus Bev had a mean DpR of 0% (interquartile range: -16%, 10%) and a minimum DpR of -111%. DpR >= 30% was associated with significantly longer OS and PFS when compared with DpR <= 30% in patients given FOLFIRI plus C-mab. DpR (>= 30%) was independently associated with prolongation of OS and PFS. In patients treated with FOLFIRI plus C-mab, there was a moderate positive correlation between DpR and clinical outcomes (OS: r= 0.51, P< 0.001; PFS: r= 0.54, P< 0.001). Conclusion: FOLFIRI plus C-mab yielded a stronger correlation between DpR and clinical outcomes. These results indicate the potential of DpR as a new measure of efficacy in mCRC patients treated with second-line chemotherapy plus C-mab.