Research shows the test could provide a reliable prediction as early as two to three weeks after starting treatment. However, scientists caution the results still need to be replicated before the test is used clinically.
The study, “Early circulating tumor DNA dynamics and clonal selection with palbociclib and fulvestrant for breast cancer,” was published in the journal Nature Communications.
“[Ibrance] is one of a new class of drugs that delays cancer progression for patients with advanced breast cancer, but it’s not effective for everybody. The problem is we have to wait for two to three months before doing a scan to see if the therapy is working,” Nicholas Turner, MD, PhD, the study’s senior author and a professor at The Institute of Cancer Research in London, said in a press release.
“Having an early indication of how likely a treatment is to work might allow us to adapt treatment — switching some patients to an alternative drug that is more likely to benefit them,” he said.
The test detects DNA mutations in breast cancer patients by analyzing fragments of circulating tumor DNA (ctDNA), which refers to cancer DNA that has entered the bloodstream.
Researchers evaluated the test in women with the most common type of advanced breast cancer — estrogen receptor-positive, HER2-negative breast cancer — who are participating in the PALOMA-3 Phase 3 clinical trial (NCT01942135) testing Ibrance and Faslodex (fulvestrant) in these patients.
A total of 73 women had a mutation in the PIK3CA gene, 52 of whom received treatment with Ibrance. PIK3CA‘s association with breast cancer has already been established.
Results showed the blood test was able to predict the success of Pfizer Oncology‘s Ibrance by comparing the amount of PIK3CA before and 15 days after start of treatment.
Investigators found that the degree of decrease of PIK3CA in ctDNA correlated with progression-free survival (PFS), which is the length of time a patient lives without their disease worsening. Women with a smaller PIK3CA decrease had a median PFS of only 4.1 months, compared with 11.2 months in those with large reductions.
“Our data demonstrates that early ctDNA changes may be predictive for cytostatic therapies such as [Ibrance],” the researchers wrote. Cytostatic medications are those able to kill cancer cells.
Nathan Richardson, PhD, head of molecular and cellular medicine at the Medical Research Council (MRC), said, “It is exciting to see that using advances in diagnostic techniques, such as genetic tests for [ctDNA], we may be able to more accurately define groups of patients and help us deliver the right treatment to the right patient sooner.”
MRC was the main funding source of the study.