By re-expressing mutant Mcl-1 constructs in Mcl-1-deficient, CIS sensitive cells and measuring ROS production under CIS conditions, we were able to show that the P198 residue, (but not any of its C-terminal anti-apoptotic Bcl-2 homology domains) is necessary for anti-ROS function. The gene discussed is MCL1; the disease is in situ carcinoma.