PHILADELPHIA — The number of alterations detected in the DNA collected from blood samples (liquid biopsies) of cancer patients treated with immune checkpoint inhibitors was associated with response to the treatment, according to results of a study published in Clinical Cancer Research, a journal of the American Association for Cancer Research.
“Immune checkpoint inhibitors, a class of immunotherapy, are transforming cancer treatment; however, overall only about 20 percent of patients respond to these drugs, and the drugs sometimes have significant side effects,” said the study’s senior author, Razelle Kurzrock, MD, director of the Center for Personalized Cancer Therapy at the University of California San Diego Moores Cancer Center. “Therefore, it is important to have biomarkers that can help predict response to these relatively new drugs.
“Our study demonstrated that high circulating tumor DNA [ctDNA, tumor DNA derived from a blood sample] alteration number was associated with response to checkpoint inhibitor therapy,” Kurzrock added.
Most biomarkers used to predict response to checkpoint inhibitors are measured on tumor biopsy specimens and have limitations, said the study’s first author, Yulian Khagi, MD, a Hematology-Oncology fellow at the University of California San Diego Moores Cancer Center. “Biopsies can be painful, expensive, risky, and not always representative of the tumor characteristics overall,” he said. “We wanted to identify an easily obtainable and easily interpretable biomarker that can predict response to checkpoint inhibitor therapy utilizing genomic sequencing of DNA that is shed from cancer cells into the bloodstream.”
Using blood samples from 69 patients with different types of cancer treated with immune checkpoint inhibitor therapy, the investigators analyzed the ctDNA by next-generation sequencing (Guardant360 assay). Specifically, they counted the number of variants of unknown significance (VUS, alterations/mutations in the DNA whose association with disease risk is unknown).
Of the 69 patients, 29 percent had more than three VUS alterations and 71 percent had three or fewer VUS in their ctDNA.
After being treated with an immune checkpoint inhibitor, patients with more than three VUS in their ctDNA had significantly higher response rates (45 percent) compared with those who had three or fewer VUS (15 percent).
“Though the study was small, a significant difference could also be identified for a longer survival without progression of cancer and even a longer overall survival in the high versus low VUS alteration group,” noted Khagi. “It is likely that, with larger studies, this difference will become more significant.” Among patients who had higher numbers of alterations of the VUS type, the median survival was not reached while those who had lower numbers of alterations of the VUS type had a median survival of only about 11 months.
“Mutations lead to the production of abnormal proteins; the more mutations and abnormal proteins the tumors produce, the better the chance that one or more of these proteins will be ‘detected’ by the immune system,” explained Kurzrock. “We showed that counting the mutations in the DNA floating in the bloodstream could help predict response to these new and exciting drugs that boost the immune system to attack cancer.”
Khagi noted, “If verified by further studies, clinicians will be able to utilize the objective results of this simple blood test to make determinations about whether to use checkpoint inhibitor-based immune therapy in a variety of tumor types. It should also be noted that the cutoff points might be different as these blood tests evolve to detect more mutations in more genes.”
The researchers noted that the study’s retrospective nature and small sample size are key limitations.
This study was funded by the Joan and Irwin Jacobs Fund and the National Cancer Institute. Khagi has no significant conflicts of interest. Kurzrock receives consulting fees from XBiotech, Loxo, and Actuate Therapeutics; has an ownership interest in CureMatch Inc; receives speaker fees from Roche; and has research funds from Incyte, Genentech, Pfizer, Sequenom, Guardant Health Inc., Foundation Medicine, and Merck Serono.