Blood test to predict how well immunotherapy works for colorectal cancer

Doctors treat some advanced colorectal cancers with immunotherapy medications that help your immune system fight cancer. This study is testing whether a simple blood test — which looks for traces of cancer DNA circulating in your bloodstream — can predict whether the immunotherapy is actually working before imaging scans show results.

Sometimes imaging scans don't show that cancer is shrinking, but surgery later reveals the cancer was actually completely gone. This blood test might help doctors understand how well the treatment is working much sooner, so they can make better decisions about your care.