Circulating tumor DNA: a resuscitative gold mine?

Tumor tissue specimens obtained by surgical or biopsy procedures remain to be the only source of the tumor DNA required for the molecular and genomic analysis of human cancers. However, such tumor tissue sampling has several clinical limitations: there are invasive procedures; a single tumor biopsy cannot reflect the intratumoral heterogeneity or the difference between primary tumor and metastasis, and it is difficult to sample frequently. Alternatively, blood-based biomarkers could overcome these limitations. However, only several clinically proven protein markers are commonly used in the diagnosis and prognosis of human cancer. In addition, these protein markers are often secreted not only by tumor cells but also by normal or benign tumor cells.