A method determines the likelihood that a subject has or will develop cancer. The method is based on identifying whether targeted somatic mutagenesis of a nucleic acid molecule by a mutagenic agent has occurred. The mutations are at one or more motifs recognized or targeted by the mutagenic agent such as AID, an APOBEC cytidine deaminase or aflatoxin, The nucleic acid molecule includes the whole exome. The cancer can be any of breast, prostate, liver, colon, pancreatic, skin, cervical, lymphoid, hematopoietic and ovarian cancer; and the biological sample comprises, respectively, breast, prostate, liver, colon, pancreatic, skin, cervical, lymphoid, hematopoietic or ovarian tissue or cells.