Blood test could spare colon cancer patients from chemo

Researchers from the Walter and Eliza Hall Institute (WEHI) and Johns Hopkins’ Sydney Kimmel Comprehensive Cancer Center have co-designed a new blood test that could revolutionise how chemotherapy is used for colon cancer, by identifying the patients that need chemotherapy and those that can be safely spared treatment.

Stage II colon cancer is defined as a cancer that has grown through the wall of the colon but does not extend to the lymph nodes or other organs. While most patients with stage II colon cancer are cured after surgery to remove the cancer from the bowel, the cancer will recur in around 20% of patients.

Chemotherapy is currently offered to all stage II colon cancer patients, despite a majority not needing it. This means that many patients are receiving the treatment and its associated toxicities without any benefit, noted WEHI clinical scientist Associate Professor Jeanne Tie.

WEHI and Johns Hopkins researchers collaborated to develop a blood test to identify patients who require chemo after surgery, by measuring levels of circulating tumour DNA (ctDNA) — genetic material shed from tumours into the bloodstream. The test was assessed as part of a clinical trial involving more than 450 patients and over 20 hospitals from across Australia, with the results published in The New England Journal of Medicine.

The goal of chemotherapy when given after colon cancer surgery is to eradicate micrometastases — cancer cells that have travelled from the original cancer in the bowel through the bloodstream to deposit in another site, such as the liver. These deposits of cancer cells are minuscule and are not seen at surgery or on radiologic images during the initial stages; however, they will gradually increase in size and become large enough to be seen on a standard CT scan if they are not treated with chemotherapy.

The new blood test can detect these invisible cells that release tiny amounts of ctDNA into the bloodstream, enabling researchers to identify which patients should be offered chemotherapy based on whether micrometastases have been detected. Previously, there was no way of determining whether all the cancer had been removed through colon surgery.

“Our trial has conclusively shown how the ctDNA blood test can be used to direct post-surgical therapy in stage II colon cancer and substantially reduce the number of patients treated with chemotherapy, without impacting the risk of cancer relapse,” Tie said.

“We found that when a patient’s blood test does not reveal ctDNA after colon surgery, the likelihood of micrometastases is very low and chemotherapy can be avoided as there are no tumour fragments left to kill.”

While previous studies have suggested ctDNA measurements could be used to determine the risk of cancer recurrence, the latest trial is believed to be the first randomised study in the world to provide the clinical evidence required to move this from a promising blood test to one that should be routinely used in clinical practice.

The researchers also hope to demonstrate the value of ctDNA-informed treatment in other stages of colon cancer and other cancer types, including pancreatic and ovarian cancer, with three additional randomised studies already underway.

Image credit: ©angellodeco/Dollar Photo Club

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