Blood test spots microscopic cancer to predict relapse risk

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A new blood test detects cancer DNA after surgery to predict a relapse and guide decisions about whether patients should receive chemotherapy.

A diagnosis of cancer can be terrifying—but sometimes the treatments themselves can be just as frightening for patients. Surgery, chemotherapy, radiation therapy, and immunotherapy can be daunting and some of the side effects from these life-saving technologies can be life-changing.

Chemotherapy is still the mainstay of most cancer treatment and has saved countless lives—but the new test is a step toward identifying when chemotherapy may not be necessary. Finding and measuring cancer DNA in patient’s blood could revolutionize cancer care, according to a new study.

The blood test is currently in clinical trials at more than 40 hospitals in Australia and New Zealand—making it one of the largest trials both in Australia and around the world that’s investigating a predictive blood test to guide cancer treatment.

Preventing cancer’s return

For the study, which appears in Gut, researchers were specifically investigating bowel cancer. At the time of diagnosis, many early stage bowel cancer patients have tumors that appear to be limited to the bowel, with no evidence they have spread to elsewhere in the body.

But, following successful surgery to remove the cancer, around a third of these patients get a recurrence elsewhere in the body in later years. That means the cancer cells had already spread at the time of diagnosis, but couldn’t be detected using current standard blood tests and scans.

If these patients had received treatment with chemotherapy after surgery to eradicate microscopic residual cancer cells responsible for the cancer’s return, it would have prevented about a third of relapses.

Currently, doctors base their decision to use chemotherapy on pathological assessment of the bowel cancer removed at the time of surgery.

For example, the discovery of cancer cells in the lymph glands next to the bowel (known as a Stage III cancer) means there is an increased probability that the cancer has already spread.

But while pathology information is useful, it lacks precision. Some high-risk patients won’t have cancer recurrence because surgery alone has cured their cancer, while other apparently low-risk patients will suffer recurrence.

This lack of ability to accurately determine who has microscopic disease and is most at risk of relapse means that many patients currently get treatment with six months of chemotherapy.

This means dealing with the sometimes tough side effects of chemotherapy, even though they may not need to have the treatment. Meanwhile, other patients that would potentially benefit don’t receive the necessary chemotherapy, because they appear to be at low risk.

Microscopic cancer

When cancer cells rupture and die, which is constantly happening in all cancers, they release their contents, including cancer-specific DNA that floats freely in the bloodstream—this is called “circulating tumor DNA.”

The detection of “circulating tumor DNA” after bowel cancer surgery indicates there’s remaining microscopic cancer cells in the patient that couldn’t be picked up by standard tests.

Researchers developed the new blood test through a collaboration between the Walter and Eliza Hall Institute at the University of Melbourne and the Johns Hopkins University Kimmel Cancer Center in the US.

The research shows that patients who test positive for “circulating tumor DNA” after surgery have an extremely high risk of cancer relapse—close to 100 percent. While those with a negative test have a very low risk of the cancer returning—less than 10 percent.

The next step is to show that using this blood test can personalize chemotherapy; avoiding unnecessary chemotherapy in those people with low-risk cancer; and improving cancer survival in those with very high-risk disease by intensifying their treatment.

The trials began in early stage bowel cancer patients in 2015 and have already shown the blood test can determine whether these patients can be divided into “high risk” and “low risk” groups. In 2017, the trial was extended to include women with ovarian cancer—and researchers hope to soon include pancreas cancer.

More than 400 patients have already joined in the trials of the ctDNA test but researchers want to recruit more than 2,000 participants. Currently 40 hospitals across all states in Australia and in New Zealand are taking part, which is expected to run until 2021 for bowel cancer and 2019 for ovarian cancer.

Source: University of Melbourne