TOP1 and colorectal cancer: Although a later study on the roles of TDP1 and TOP1 in modulating colorectal cancer response to irinotecan demonstrated that TDP1 overexpression or TOP1 depletion is protective, while conversely TDP1 depletion leads to TOP1-dependent hypersensitivity to irinotecan, there was no correlation between inherent TDP1 or TOP1 protein levels alone and irinotecan sensitivity [28].