A new study from Washington University School of Medicine in St. Louis demonstrates that a liquid biopsy examining blood or urine can help gauge the effectiveness of therapy for colorectal cancer that has just begun to spread beyond the original tumour. Such a biopsy can detect lingering disease and could serve as a guide for deciding whether a patient should undergo further treatments due to some tumour cells evading an initial attempt to eradicate the cancer.
While a few liquid biopsies have been approved by the US Food and Drug Administration, mostly for lung, breast, ovarian and prostate cancers, none has been approved for colorectal cancer.
Patients in this study had what is known as oligometastatic colorectal cancer, meaning each patient’s cancers had spread beyond his or her original tumour but only to a small number of sites. Such patients undergo chemotherapy to shrink the tumours before having surgery to remove whatever remains of the primary tumour. There is debate in the field about whether, after initial therapy, oligometastatic cancer should be treated like metastatic cancer, with more chemotherapy – or like localized cancer, with more surgery plus radiation at those limited sites.
Contributing to the problem is that doctors have a limited ability to predict how patients will respond to early chemotherapy, especially since most patients don’t have access to cancer genome sequencing to identify the DNA mutations in their original tumours.
“Being able to measure response to early chemotherapy without prior knowledge of the tumour’s mutations is a novel idea and important for being able to determine whether the patient responded well to the therapy,” said senior author Aadel A. Chaudhuri, MD, PhD, an assistant professor of radiation oncology. “This can provide guidance on how to treat oligometastatic disease. For example, if the liquid biopsy indicates that a patient responded well to the early chemotherapy, perhaps they should be offered the possibility of more surgery, which could potentially cure their disease. But if they didn’t respond well, it’s likely the cancer is too widespread and can’t be eradicated with surgery, so those patients should receive more chemotherapy to control their disease.”