“Liquid Biopsy” Inexpensive blood test to spot early stage cancers

A “liquid biopsy” is a blood test that can spot early-stage cancers by identifying circulating tumor cells or cell-free DNA from tumors that has been shed into the blood. Examining DNA for mutations typical of malignancies has yielded a relatively high false-negative rate. Investigators decided to look not at DNA structure (i.e., mutations) but rather at the pattern of genes that were turned on or off (i.e., methylation status).

Their technology could accurately detect the methylation pattern of very small amounts of circulating tumor DNA. Moreover, the methylation pattern of circulating tumor DNA matched the methylation pattern of the primary tumor tissue in the same patient. Seven different malignancies (e.g., lung, breast) were tested, and each had a characteristic methylation pattern. The technology then was tested in a new group of 199 patients with one of three different types of cancer and in 62 healthy controls. The accuracy of the test was very high (very few false negatives or false positives), even in patients with early-stage cancers.