Tumor-derived DNA can be detected in plasma, urine,or stool samples.• Alterations in DNA can be assessed by loss ofheterozygosity, mutations, microsatellite DNAalterations, and DNA methylation patterns.• Allelic imbalance (AI), or the loss or gain ofchromosomal regions, can be detected in a variety ofcancers, and may be a useful marker for diagnosis andcancer progression, in combination with CA-125.