Liver lessions

My husband just recently had a CT scan after 4 rounds of FOLFOX which said that 5 of the lessions were stable but the largest one had shrunk from 20 mm to 13 mm. We thought it was strange that 5 of the lessions did not change at all and only 1 showed a response. Has anyone else ever had a similar response? Just trying to figure it out. Thanks for your comments.