Non-invasive Tests for Cancer — Liquid Biopsies


By Merry Morris

Imagine a simple blood test that could detect cancer so early that it’s quite curable. What a reassurance to a cancer surgery patient whose test confirms no residual cancer throughout his body!

Liquid Biopsies – Promise and Challenges

Cancer detection from a standard blood draw is becoming a reality. Because cancer cells shed their DNA into the bloodstream, traces of the cancer as well as actual cancer cells are there for the finding. What makes detection so extraordinarily difficult, especially in cancer’s earliest stages, is the presence of a lot more normal DNA.

But super-early detections are now within medicine’s grasp thanks to advances in rapid DNA sequencing. Earlier attempts at pinpointing cancer DNA were plagued by technical limitations like high background noise and error rates. With improved techniques, the results from decoding millions of the patient’s short DNA fragments can be compared against the map of the human genome to highlight particular arrangements of DNA that indicate a specific cancer.

Dennis Lo of the Chinese University of Hong Kong, a long-time researcher in this area, is currently conducting large-scale tests to pinpoint liver and nasopharyngeal cancers, both relatively common cancers in China. A number of researchers are now competing to create a “pan-cancer” test that would detect several common cancers.

Guiding Cancer Therapy

When a cancer patient is prescribed specialized drugs to fight a particular tumor, doctors assume that the right drug is being administered. What if that tumor mutates during treatment? Will the existing drug be effective then? Not necessarily, asserts Helmy Eltoukhy, CEO of California-based diagnostics startup Guardant Health. “Seventy five percent [of patients] are on treatments that are not working for them,” he says. However, repeating these rapid-sequencing-based tests during the course of an individual’s therapy can alert that a genetic change has occurred and a different chemotherapy drug is needed. That saves the patient from therapies that are doing no good, while the cancer progresses to untreatable levels.

Early Detection, Early Attention

The recent increase in cancer survival rates has been largely the result of early detection and treatment. For the fortunate patient whose cancer will be found early on with the help of a “liquid biopsy,” the benefits are startling. Consider one statistic: More than 90 percent of women diagnosed with the earliest stage ovarian cancer survive their disease for at least five years compared to around five percent for women diagnosed with the most advanced stage of disease.

Extension Questions

  • Research cancer survival rates. How do the current survival rates compare to those of 20-, 30-, or 40-years ago?