In 10 seconds? A blood test for tumor DNA might be a better way to decide what treatments are best for colon cancer patients.
A blood test for tumor DNA? What’s that all about? Circulating tumor DNA (ctDNA) is the star of today’s digest. First, let’s break down what that is. DNA, the genetic material that is located in the nucleus of our cells, is unique to each individual and is pretty much the same among all the healthy cells in our bodies (with some exceptions). For cancer to form, multiple mutations must occur in the DNA of those cells, making tumor DNA distinct from the DNA inside of our healthy cells.
OK. Seems straightforward so far. Great! As tumors grow, it’s common for a proportion of the tumor cells to die. During cell death, the tumor cell will break open and release its cellular contents (like DNA). Some of the tumor DNA will end up in the bloodstream and this is called ctDNA. ctDNA is being actively investigated for its utility as a biomarker for cancer.
What are biomarkers? “Biomarker’ is a term that scientists use to refer to measurable biological features (eg. Presence/absence of a specific mutation, antibody, enzyme, etc.) that can be assessed to serve a scientific or medical purpose. Frequently when biomarkers are discussed in the context of cancer, it’s to determine whether certain biological features can be used to assess cancer risk, detect cancer early, or, as is the case in this study, to assess if aggressive cancer treatment is necessary.
OK so what’s this study all about? Researchers were trying to figure out a better way to determine if early stage colon cancer patients should receive chemotherapy or not after surgery. This is because surgery alone can successfully treat about 80% of early stage colon cancers. While doctors may offer chemotherapy after surgery to keep the risk of cancer recurrence (AKA cancer coming back) as low as possible, they also want to ensure that patients don’t receive any unnecessary treatments, which may be pricey and have nasty side effects.
That makes sense. So? As it stands now, the decision to offer patients chemotherapy or not after surgery is based on a relatively subjective ruling of whether that patient’s tumor exhibits ‘high-risk features’. But subjectivity doesn’t sit well with scientists. Researchers in this study knew that colon cancer patients who had detectable ctDNA in their blood after surgery had a high risk of recurrence. Based on these data, they wondered if presence or absence of ctDNA in patients after surgery would be a superior biomarker to determine whether or not patients should receive chemotherapy or not after surgery.
What did they find? In the study, patients with ctDNA present in their blood after surgery received chemotherapy and those without ctDNA did not. They found that this method ultimately reduced the number of patients who received chemotherapy without increasing the risk for cancer recurrence after surgery. Furthermore, this study provided evidence that chemotherapy in patients with ctDNA in their blood after surgery is helpful in preventing cancer recurrence for early stage colon cancer, which was not previously established.
Sounds great! But are there any drawbacks? This study showed that the ctDNA-guided approach to cancer treatment was non-inferior to standard cancer management. It ultimately did not improve overall survival, but rather, lowered the number of patients who received chemotherapy without negatively impacting survival. Plus, the capacity to perform ctDNA analysis is not widely available in cancer care facilities. So there’s room for improvement. Nonetheless, this study is exciting because it shows a simple blood test can help doctors make educated life saving decisions for cancer patients!
Why is ctDNA a good biomarker?
Cancers are deemed to be early-stage if they have not yet visibly spread beyond their point of origin. Sometimes, however, cancer stages are mischaracterized if cancerous cells have begun to spread in unseen ways.
Since DNA is supposed to be protected within the nucleus of our cells, ctDNA only survives a short period of time in our bloodstream (a half-life of 2 hours). That’s why after surgery is performed to remove cancer, ctDNA can be a useful indicator that the cancer is still present –even if there are no visible signs!
Dr. Talia Henkle has distilled 3 papers saving you 10.5 hours of reading time.
The Science Integrity Check of this 3-min Science Digest was performed by Flávia Oliveira Geraldes