DNA shed from colon cancers into bloodstream guides chemotherapy post surgery

A new research study showed that circulating tumor DNA (ctDNA)-genetic material shed from tumors into the bloodstream-can identify stage II colon cancer patients who can most benefit from chemotherapy following surgery and spare other patients the need for this form of treatment.

It was found that testing for ctDNA after surgery and directing chemotherapy to ctDNA-positive patients reduced the use of chemotherapy overall without compromising recurrence-free survival.

There are several prior research studies demonstrating that circulating tumor DNA can be detected in blood and that the presence of ctDNA post-surgery predicts risk of cancer recurrence. However, this is believed to be the first clinical study showing that the measurement of circulating tumor DNA prior to therapy may benefit patients.

Currently, the use of chemotherapy in stage II colon cancer, which is defined as colon cancer that has grown through the wall of the colon but does not extend to the lymph nodes or other organs, is controversial. This study was aimed at helping solve the controversy by assessing whether ctDNA could be used to provide a more precise prediction of recurrence risk after surgery.

In the study, 455 patients with stage II colon cancer were randomized after surgery 2:1 to standard treatment or ctDNA-guided management. Of these patients, 153 received standard management, which includes monitoring over time for recurrence or chemotherapy.

An additional 302 patients underwent blood tests within seven weeks after surgery to search for ctDNA. If ctDNA was detected, patients received fluoropyrimidine or oxaliplatin-based chemotherapy. If ctDNA was not detected, patients did not receive chemotherapy.

The goal of chemotherapy in colon cancer is to eradicate micrometastases, cancer cells not yet visible on radiologic images that travel through the bloodstream and cause cancer to come back or spread to other parts of the body. Using ctDNA to detect these invisible cells can now identify which patients are most likely to have micrometastases and, therefore, are most likely to benefit from chemotherapy.

The researchers hope these findings will stimulate the study of ctDNA in patients with other stages of colon cancer and other types of cancer. In future studies, the researchers will explore patients with early-stage pancreatic cancer and stage III colon cancer to see if ctDNA can similarly identify patients who are most likely to benefit from more aggressive chemotherapy than is currently used. They also plan to explore whether the presence of residual ctDNA can be used to help optimize the management of individual patients following surgery or other forms of therapy