A newly discovered clue in blood could help detect both tumor cells and their location in the body.
Traditional cancer blood tests help identify DNA released by dying tumor cells in a patient’s blood. This can establish whether a person has cancer or not. Although they are the current first-line method for screening for cancer, these tests do not identify where a cancer resides. For some forms of cancer, the way to do so is by performing a scan or an invasive biopsy. A new blood test that could do just that has been developed at the University of California San Diego (UCSD).
Once a tumor begins to grow in the body, it competes with healthy cells for nutrients and space. In doing so, the healthy cells die and release their DNA into the blood. A specific section of this released DNA changes dependent on the healthy cell’s tissue of origin. The test searches for these specific DNA sequences to help understand where a tumor resides in the body.
To create their new method, the researchers built a database of DNA sequences specific to 10 different normal tissues. These included liver, intestine, colon, lung, brain, kidney, pancreas, spleen, stomach and blood.
In addition, the team created a second database of cancer-specific markers by analyzing tumor and blood samples from cancer patients at the UCSD Moores Cancer Center.
Researchers then screened blood samples from people with and without tumors, searching for cancer-specific markers and tissue-specific DNA sequences.
The test acts as a two-part diagnostic tool – cancer is present if specific markers are found, while its location is determined by which DNA sequence is present.
Although currently at a proof-of-concept stage, the technique could prove a revolutionary method for diagnosing cancer.
Understanding where a tumor originates in the body can help guide treatment decisions at an earlier stage, without the need for extensive invasive testing or scans. Knowing a cancer’s origin without extensive testing means treatment can start sooner, potentially improving chances of survival.
This is particularly applicable to cancer of unknown primary (CUP) where the place the disease began cannot be determined.
In normal cancer cases, the origin of a cancer can be determined by the visible characteristics of the cells themselves. For example, a tumor formed of breast cells found in the lungs is likely to have originated from the breast. In this instance, the person would be diagnosed with breast cancer and treated using methods known to effectively treat breast cancer.
In cases of CUP however, the cells may not indicate their tissue of origin. This means the patient may need to undergo extensive diagnostics procedures, including biopsies, blood tests, scans and possibly surgery to determine a diagnosis. In most cases, a definitive diagnosis is never made.
Treatment for CUP is a trial and error process as doctors are unsure as to how therapy will affect the cancer cells. This potentially exposes CUP patients to unnecessary toxic effects.
Guo, Shicheng, Dinh Diep, Nongluk Plongthongkum, Ho-Lim Fung, Kang Zhang, and Kun Zhang. Identification of methylation haplotype blocks aids in deconvolution of heterogeneous tissue samples and tumor tissue-of-origin mapping from plasma DNA. Nature Genetics, 2017; 49 (4): 635-642