Background: Molecular-targeted drugs are known to have angiogenesis-inhibiting properties, and thus can inhibit angiogenesis inside the tumor tissue to cause necrosis, even if the tumor diameter is unchanged. We retrospectively investigated relationship between imaging change associated with regorafenib (REGO) treatment and the treatment outcome in Japanese mCRC. Methods: Eligibility included ECOG-PS 0 or 1, treated with REGO with lung or liver metastasis, started dose with 120 or 160mg/day of regorafenib and duration of treatment (DOT) must be 35 days or more (excluding interruption). Patients (Pts) were performed baseline CT within 28 days before and first CT assessment were between eight and 12 weeks after start of regorafenib. The main objective of this analysis is to investigate the correlation between the imaging change and outcome. As imaging change, onset or increase of Cavitation of lung lesion (CLL), morphologic response of liver lesion (MRL), Change of liver metastasis density (CLD) were evaluated. In all cases, independent two radiologists are evaluating radiological change after regorafenib treatment. Results: We finally screened 671 cases and 231 cases were eligible. The pts background was male/female 147/84, median age　64.0 (range: 32-83), median DOT of REGO　86 days (range: 35-818). The pts with lung metastasis were 153, and with liver metastasis were 166. CLL were positive in 69 (40.0%) pts. The median progression free survival (PFS) of the pts with/without CLL were 3.2/2.4 months (HR 0.794; 95% CI 0.584-1.080). Median overall survival (OS) of the pts with/without CLL were 10.5/9.0 months (HR 1.058; 95% CI 0.751-1.489). Median OS of pts with/without CLL in female were 11.4/7.9 months (HR 0.630; 95% CI 0.352-1.127). The MRL and CLD of liver metastasis were analyzed in 147 / 91 pt. Median OS of pts with/without MRL were 9.9/8.2 months (HR 1.015; 95% CI 0.581-1.774) and Median OS with/ without CLD were 11.6/7.0 months (HR 0.604; 95% CI 0.353-1.031). Conclusions: Cavitation of lung metastasis may predict PFS of the pts but not OS. Change of Liver metastasis density were predictor of favorable outcome to regorafenib. (UMIN000023329).