TP53 and neoplasm: Interestingly this potent tumor growth inhibition was difficult to demonstrate in vitro as when we treated Brca1−/−;Trp53R172H/− and Brca1−/−;Trp53−/− cells with up to 50 μM, we found the cell lines were relative resistant and showed only mild increases in pChk1, p21 and CC3 after 6 h that decreased by 24 h (Supplemental Fig. S4A and B).