A new blood test can locate the presence of a tumor in a particular tissue, which may circumvent the need for invasive procedures such as biopsies and aid in cancer diagnosis according to a recent study published in Nature Genetics.1
Cancer blood tests detect cancer by screening for traces of DNA released by dying tumor cells. However, they do not provide information about the location of the tumor. “Knowing the tumor’s location is critical for effective early detection,” said Kun Zhang, a bioengineering professor at the University of California San Diego Jacobs School of Engineering and an investigator on the recent study.
The investigators identified the location of a tumor using CpG methylation haplotype, a type of DNA signature. CpG methylation is the addition of methyl groups to CG sequences in DNA. Each tissue can be identified by its unique collection of methyl groups, known as a methylation haplotype. As a tumor grows it competes for nutrients and space in the tissue, causing normal cells to die. DNA from dying normal cells released into the bloodstream can then be used to identify tumor location using methylation haplotype.
“We made this discovery by accident. Initially, we were taking the conventional approach and just looking for cancer cell signals and trying to find out where they were coming from. But we were also seeing signals from other cells and realized that if we integrate both sets of signals together, we could actually determine the presence or absence of a tumor, and where the tumor is growing,” explained Zhang.
The researchers created 2 databases: one of tissue CpG methylation patterns (liver, intestine, colon, lung, brain, kidney, pancreas, spleen, stomach, and blood), and the other of cancer-specific genetic markers. The test requires both cancer-specific genetic markers and a tissue specific methylation pattern above a statistical cutoff to assign a positive match.
1. Guo S, Diep D, Plongthongkum N, et al. Identification of methylation haplotype blocks aids in deconvolution of heterogeneous tissue samples and tumor tissue-of-origin mapping from plasma DNA. Nat Genet. 2017 Mar 6. doi: 10.1038/ng.3805 [Epub ahead of print]