2017-11-01
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Date: October 2, 2017
Source: University of California - San Diego
"We can help predict response to immunotherapy by measuring the number of mutations in circulating tumor DNA using a simple blood test," said Yulian Khagi, MD, UC San Diego Moores Cancer Center fellow and first author. "Immunotherapy can result in serious side effects, and therefore being able to predict who will respond is important to mitigating potential risk to each patient."
The findings, publishing in the journal Clinical Cancer Research on Oct. 2, show that 45 percent of patients with more than three genomic alterations (specifically, variants of unknown significance) detected in the tumor DNA that circulates in the bloodstream -- known as ctDNA -- responded to checkpoint inhibitor-based immunotherapy. Patients with fewer alterations had a 15 percent response.
"Checkpoint inhibitor immunotherapy is exciting, but it is currently given to patients with all types of cancer, and most of the time it is not known if it will result in a response," said Razelle Kurzrock, MD, director of the Center for Personalized Cancer Therapy at UC San Diego Moores Cancer Center and senior author of the study. "Indeed, more than 80 percent of patients with cancer fail to respond to checkpoint inhibitor immunotherapy."
Patients with a high number of alterations also had longer progression free survival, or the period of time in which a patient lives with cancer without it advancing. Those who responded to immunotherapy at two months and had high numbers of genomic alterations in the blood had a median response last nearly two years.
"Considering that many of these patients had advanced disease that was resistant to many other therapies, this result is impressive," said Kurzrock.
Study findings mirror what has been previously described in genomic testing of tissue samples. However, in this report, the result was obtained from a small tube of blood without a tissue biopsy.
Once reactivated with the use of checkpoint inhibitor immunotherapy, the immune system needs to recognize cancer cells. The more mutations a cancer cell harbors, the more it stands out compared to normal tissue, and the easier it is for the immune system to recognize and target a tumor.
