Abstract: A method is provided for identifying a subject likely to have, or at risk of developing a disease condition correlated with increased reactive oxygen species (ROS), including cancer, by identifying in the subject a missense mutation in a nucleic acid of Complex III, IV and/or V of the OXPHOS system. This invention also provides a method of identifying a likelihood of having a heritable predisposition to cancer by detecting a homoplasmic missense mutation in non-tumor tissue of an OXPHOS system gene. This invention also provides a method for detecting likelihood of having cancer, predisposition to cancer, and likelihood of passing a predisposition to cancer to progeny involving identifying in non-tumor tissue of the subject a missense mutation in a complex III, IV and/or V gene of the mitochondrial OXPHOS system. The mutation may be a nuclear or mitochondrial mutation. The invention has been exemplified with respect to prostate cancer.