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People with prostate cancer whose tumors contain a shortened protein called AR-V7, are less likely to respond to two widely used drugs for metastatic prostate cancer, according to a new study. The shortened protein can be detected in the blood. 

According to researchers, if the findings are validated through large-scale studies, men with detectable blood levels of AR-V7 could avoid these two drugs and instead take other medicines to treat their prostate cancer. 

Enzalutamide and abiraterone have been very successful in lengthening the lives of about 80 percent of patients with metastatic prostate cancer, said Emmanuel Antonarakis, M.D., assistant professor of oncology at Johns Hopkins in the press release, but the drugs do not work in the remaining 20 percent of patients.

"Until now, we haven't been able to predict which patients will not respond to these therapies. If our results are confirmed by other researchers, a blood test could use AR-V7 as a biomarker to predict enzalutamide and abiraterone resistance, and let us direct patients who test positive for AR-V7 toward other types of therapy sooner, saving time and money while avoiding futile therapy," added Antonarakis.

Researchers, however, underscored the fact that most of the study patients had advanced disease and received multiple prior therapies, so the outcomes may not be generalizable to all men with prostate cancer.

"Patients whose blood samples contained AR-V7 got no benefit from either enzalutamide or abiraterone," said Antonarakis. He added that shortened AR-V7 protein could appear in patients' blood samples at the very start of therapy or acquired later, after therapy has begun.

"This test could be used before starting enzalutamide or abiraterone therapy, and if the test shows the presence of AR-V7, patients may opt for a different therapy. It could also be used to monitor patients receiving enzalutamide or abiraterone for AR-V7, providing an indication these drugs may not work for much longer."

The study has been described in the New England Journal of Medicine.