- Failure of early
detection of cancers leads to high mortality and morbidity.
- New blood based
test detects early stage cancers with an overall success of 62%.
- Researchers claim
that smokers and women with inherited breast cancer mutations are the ones
who would benefit the most from the new development.
While cancer cases are rising at an alarming rate every year, early
detection of the cancers is still a relatively difficult phenomenon. In fact,
much of the morbidity and mortality in human cancer is related to the late
diagnosis of this disease, where surgical and pharmacologic therapies are less
effective. A recent study conducted at the Johns Hopkins Kimmel Cancer Center, reported a test that uses
small amounts of cancer specific DNA in blood to detect early stage cancers.
The study is published in the journal Science Translational Medicine
How is the cancer detected?
is based on isolating cell free tumor DNA (ctDNA)
Apart from DNA which is present
in our cells, some DNA is present outside the cells, in the bloodstream, which
is called free circulating DNA (cfDNA).
in tumor patients, cfDNA includes ctDNA that breaks away from the primary tumor
and enter the bloodstream and is circulating.
‘The blood based DNA test was successful in detecting 62 percent of overall early stage I and stage II cancers.’
healthy individuals there is a low level of cfDNA due to immune cell clearance.
However, in tumor patients, the ctDNA is present in higher levels in the blood
as they evade immune cells. This, if detected and sequenced will give
information on the type of primary tumor present in the body.
How specific is the test?
recently, the clinical utility of ctDNA for the detection of cancer was not
well explored due to limited sensitivity of current technology. Low levels of
ctDNA present in blood and unknown driver mutations were the key problems.
research team at John Hopkins has developed an approach called targeted error
correction sequencing (TEC-Seq) that allows ultrasensitive direct evaluation of
the tumor causing mutations in circulating cell-free DNA. This is based on deep
sequencing or reading of the DNA which means more than 30,000 reads. Scientists
claim that the test can distinguish accurately between tumor-derived DNA and
other altered DNA that are mistaken for cancer
This helps in greatly reducing false positives.
the test, scientists obtained 200 blood samples of patients with breast, lung,
colorectal and ovarian cancer
The test screened the samples for 58 genes
that were widely linked to the cancers. Overall, the test was successful in
detecting 62% of stage I and II cancers. Also, 44 healthy individuals were also
tested and none of them showed positive results for the test.
the test needs to be validated in a larger cohort to understand its efficacy.
Advantages of the test
- Blood collection for cancer detection is non-invasive
and can be done on spot. Useful in situations where collecting a solid
tumor sample is too invasive, or if there is not enough sample to detect
- Gives clear indication of presence and type of tumor at
any given point of time.
- Beneficial for high-risk
smokers for whom CT scans for lung cancer often lead to false positives.
- Also provides an easy and
convenient form of testing for women with known hereditary breast cancer
- Phallen, J., Sausen, M., Adleff, V., Leal, A., Hruban, C., White, J., Anagnostou, V., Fiksel, J., Cristiano, S., Papp, E., Speir, S., Reinert, T., Orntoft, M., Woodward, B., Murphy, D., Parpart-Li, S., Riley, D., Nesselbush, M., Sengamalay, N., Georgiadis, A., Li, Q., Madsen, M., Mortensen, F., Huiskens, J., Punt, C., van Grieken, N., Fijneman, R., Meijer, G., Husain, H., Scharpf, R., Diaz, L., Jones, S., Angiuoli, S., Ørntoft, T., Nielsen, H., Andersen, C. and Velculescu, V. (2017). Direct detection of early-stage cancers using circulating tumor DNA. Science Translational Medicine, 9(403), p.eaan2415.