CHICAGO (Reuters) - Counting bits of prostate cancer found in a patient's bloodstream may help doctors better predict which drugs work, U.S. researchers said on Saturday.
They said men in a large clinical trial of Johnson & Johnson's newly approved drug Zytiga who had the lowest levels of circulating tumor cells -- cells that break off from the main tumor and float around in the bloodstream -- were more likely to survive than men who had more of these cells.
In a separate study, a consortium of lung cancer experts studied tumor samples from 830 patients and found that about half of them had at least one of 10 genetic mutations known to drive lung cancer and could be used to guide doctors' treatment decisions.
The studies, presented at American Society of Clinical Oncology meeting in Chicago, are part of the search for biological signals known as biomarkers that can predict which patients are the best match for drugs or give an early indication that treatments are working.
The hope is these types of tests will speed effective treatments to patients and shorten clinical trials by giving researchers earlier signals that experimental drugs are working.
In the prostate cancer study, a team led by Dr. Howard Scher of Memorial Sloan-Kettering Cancer Center in New York looked to see if tests that trap circulating tumor cells -- tiny bits of cancer cells -- could show whether patients are responding to a drug.
So far, Johnson & Johnson's Veridex unit has the only approved system for capturing these rare cells, but other teams are working on them.
Scher's team analyzed a study of 1,195 men with advanced prostate cancer that showed Zytiga, known chemically as abiraterone, extended patients' lives.
Scher's team looked to see if there was a correlation between men who fared best in the trial and levels of prostate tumor circulating in their blood.
The team tested the blood of 972 patients at the beginning of the trial, and 723 patients after three months.
They found that abiraterone cut the number of circulating tumor cells, and the men who had lower levels of tumor in their blood were more likely to survive.
Scher said the study will be used to develop tests to predict whether prostate cancer drugs are working.
In the lung cancer study, researchers from a consortium of U.S. cancer centers set out to collect 1,000 tumor samples from patients with a type of lung cancer known as adenocarcinoma.
Tests of the first 830 patients found that 54 percent had a mutation that drives tumor growth.
"Driver mutations control cancer growth," Dr. Mark Kris, chief of the Thoracic Oncology Service at Memorial Sloan-Kettering Cancer Center, told the press conference. "If you negate the effects of those mutations in lab experiments, the cancer dies."
In the study, 97 percent of the driver mutations were the primary driver of the cancer, making them useful for selecting specific drugs, he said.
Kris said many centers do not routinely test patients to see which type of mutation is driving their lung cancer, partially because of cost. But he said having this information can help doctors make treatment decisions and may even serve as a model for treating lung and other cancers.
Reporting by Julie Steenhuysen; Additional reporting by Deena Beasley; Editing by Xavier Briand