Feasibility of implementation of the early tumor shrinkage as a potential predictive marker to daily clinical practice in patients with RAS wild type metastatic colorectal cancer, treated with cetuximab - a non-interventional observational study.

These findings indicate that the basic time parameter of ETS could not realistically be employed in routine oncology care of patients with metastatic colorectal cancer (mCRC) in the Czech Republic, unless there would be a strict request to perform TRFC by week 8 since the initiation of the therapy. In addition, the frequency of objective tumor response to first-line therapy with cetuximab + chemotherapy was evaluated. Based on the relative regression in the sum of diameters of measurable metastatic lesions, unconfirmed partial responses were achieved in 42.4 % and unconfirmed complete response in 8.6% of patients, altogether corresponding to the overall response rate of 51% with first-line therapy. The frequency of responses was higher among patients with left than right sided primary tumors. It seems that the regimen of cetuximab/FOLFOX might be more active in frontline therapy of right sided RAS wild type mCRC than cetuximab/FOLFIRI.