Tracking ‘hidden DNA’ in blood could help some cancer patients avoid chemotherapy

(ORDO NEWS) — Chemotherapy is an incredible tool for killing cancer cells, but our normal cells are caught in the crossfire, which can lead to life-threatening side effects.

Chemotherapy, or chemotherapy for short, is not always required for successful treatment, but how to determine if someone needs it can be both an art and a science. Now a new study offers doctors a technique that has already helped some patients with stage II colon cancer avoid chemotherapy without changing clinical outcomes.

The new study used a technique that uses a type of DNA called circulating tumor DNA (ctDNA). This is a fairly simple explanation – these are small areas of fragmented tumor DNA that circulate in the bloodstream. It is important to note that they are not part of the tumor cell, however, they are simply the DNA of the tumor itself.

This work is not the first to study ctDNA, and researchers know that the presence of ctDNA in the bloodstream after surgery predicts the risk of cancer recurrence.

However, a new study has taken this knowledge one step further. Looking at stage II colon cancer, this is the first clinical study to show that a “guided approach” to ctDNA after surgery can bring significant benefits to patients.

“Stage II colon cancer presents a unique challenge,” explains Johns Hopkins University gastroenterologist Ann Marie Lennon.

“In stage I colon cancer, patients do not receive chemotherapy because the prognosis for survival is over 90 percent. The risk of discomfort and toxicity of therapy outweighs the benefits it can bring. On the other hand, every patient with stage III colon cancer is currently receiving chemotherapy because the risk of recurrence is high.”

In stage II colon cancer, the cancer has spread through the muscle layers of the colon wall but has not yet spread to other organs. In this case, the patient will undergo surgery to remove the tumor, but then the doctor will have to make a choice whether to give him chemotherapy after that.

We know that approximately 75 percent of people with stage II colon cancer do not need chemotherapy after surgery, but about 25 percent do. Figuring out which patients will benefit the most from chemotherapy is incredibly important, and a mistake can be deadly.

Currently, there are a number of signs of a tumor that may prompt a doctor to prescribe chemotherapy – for example, if the tumor looks abnormal under a microscope or if the cancer has invaded other tissues.

However, a new study has shown that this method is not reliable, and many cancer patients may receive chemotherapy when they do not need it.

Between 2015 and 2019, 455 patients with type II colon cancer were included in the study. Of these, 302 patients were referred for ctDNA treatment, while the rest received standard treatment. Patients were followed up approximately 37 months later, meaning the study had more than three years of patient data.

Both standard and referral treatments experienced similar survival and cancer-free rates (92.4 vs. 93.5 percent) during the study period.

However, the big difference was in the amount of chemotherapy administered. In the standard treatment group, 27.9 percent of patients completed chemotherapy, while in the ctDNA group, only 15.3 percent.

This is almost twice as many patients who received chemotherapy, but without an increase in survival or a decrease in the rate of tumor recurrence.

“The ctDNA approach to treating stage II colon cancer has reduced the use of adjuvant chemotherapy without sacrificing relapse-free survival,” the researchers, led by Walter and Eliza Hall Institute gastrointestinal oncologist Jeanne Tie, write in their new paper.

“The low recurrence rate in ctDNA-positive patients treated with chemotherapy suggests that adjuvant therapy promotes survival.”

The researchers hope that ctDNA could be a useful indicator for treating other types of cancer and other stages of colon cancer, and the team is already working on early-stage pancreatic and stage III colon cancers to see if ctDNA can help there as well.

“We have the opportunity to change clinical practice,” says biomedical engineer Joshua Cohen, one of the researchers at the Johns Hopkins University School of Medicine.

“If using ctDNA to guide treatment, a patient with stage II colon cancer who tests negative for ctDNA is less likely to have cancer recurrence than the average patient with stage I colon cancer.”

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