HCT116 colon cancer xenografts: diffusion weighted MR imaging to assess early chemotherapeutic response

Objective: To assess early chemotherapuetic response in a mouse colon cancer model using diffusion weighted imaging(DWI) shown as apparent diffusion coefficient(ADC) and analyze the potentially associated histopathologic characteristics.Materials and Methods: Thirty-two Athymic mice bearing HCT116 xenografts on right rear flank were allocated into four groups: control,5Fu,oxaliplatin and 5-Fu/oxaliplatin combined.Mice were undergone body MR examination,including T2-weighted,T1-weighted and DW MR imaging,before and 3,7,11,20 days after treatment.Changes in ADC and volume of tumors were recorded and calculated.At each time point after chemotherapy,histopathological characteristics were recorded and analyzed.The correlations between changes in ADC and histopathological characteristics at each time point were analyzed.Results: the mean ADC value in each group decreased 3 days after initialization of therapy which may be associated with cell swelling without necrosis.Seven and eleven days after initialization of therapy,mean tumor ADC value in groups treated with oxaliplatin and 5-Fu/oxaliplatin combined increased and significances were seen(P0.05).For the group treated only with 5Fu,the mean ADC values 7 to 11 days after initialization of therapy increased but no significance was seen(P=0.07).Necrosis within tumor was detected 7 and 11 days after chemotherapy.However,no significant difference in ADC values between 20 days after and before therapy was shown.Regeneration in tumor was detected 20 days after chemotherapy.Conclusions: DWI shown as ADC values increased has a potential in early prediction of response to chemotherapy.