In this study, the scientists analyzed the blood of patients with bladder cancer who had been treated with immunotherapy. The subjects were part of a high-risk group and had an increased chance of disease recurrence, which put them on the waitlist for bladder removal surgery as a precautionary measure.
The scientists investigated the freely circulating DNA in the subjects' blood: small pieces of DNA that move through the bloodstream. Sometimes these contain mutated DNA from a tumor.
"This is because a tumor has undergone genetic changes compared to normal tissue," explains principal investigator Michiel van der Heijden. "Cancer cells release small pieces of DNA into the bloodstream and urine that differ from the regular DNA. In our study, we investigated whether we could still trace tumor DNA in these patients and whether we could use these measurements to predict whether the tumor would return or not.
The results of the study are promising. Based on the results of the blood tests, the researchers were able to correctly predict whether patients would recover after immunotherapy in most cases.
Small pieces of mutated DNA from the tumor were often found in patients who did not respond well to the therapy. In the patients who did respond well to the immunotherapy, no tumor DNA could be found in the blood after the treatment. This last group also saw significantly less tumor recurrence.
"We seem to be able to predict the course of bladder cancer with great precision using this technique," says Van der Heijden. "That might help prevent radical surgery for a number of patients. Patients whose blood no longer contains tumor DNA may no longer need surgery at all.”
This is a major breakthrough because cystectomies are quite invasive. "The bladder is removed during surgery, which means that patients won’t be able to urinate normally anymore," he says.
It does happen that no more tumor cells are found during surgery, indicating that the procedure may not have been necessary.
"With the tools we’ve had at our disposal thus far, we couldn’t determine whether people had really been cured," Van der Heijden explains. "No matter what kind of scans you use, you can't see exactly whether a tumor is completely gone after immunotherapy.
"This technique seems to bring improvement, and we may operate less often as a result. That's fantastic news. We will need to conduct the right follow-up studies, however, before we can apply this to clinical practice."