(Reuters Health) - Cancer drugs that keep tumors from growing may not lead to better quality of life for patients, a new study suggests.

“In countries where patients need to pay co-pays, they can use up all their savings in order to get access to those expensive new drugs and in the end, they may not extend their lives or improve their quality of life,” Feng Xie, a professor of health economics at McMaster University, told Reuters Health.

Xie and colleagues reanalyzed data from nearly 40 randomized trials involving multiple cancer types. They found that “progression-free survival,” or the length of time doctors could keep the cancer under control, was not linked with health-related quality of life.

These days, cancer researchers and drug companies often use progression-free survival as a measure of a new drug’s effectiveness, Xie explained by phone.

“In the past, when a new drug was developed, overall survival” - that is, how long the patient lived - “was the endpoint to evaluate. A lot of drugs have now been approved based on the benefit of progression-free survival,” Xie said.

One reason for using progression-free survival as a marker of effectiveness is that it can be measured sooner than overall survival, so new drugs can make it through the pipeline quicker, Xie and colleagues explain in JAMA Internal Medicine.

The problem, Xie said, is that progression-free survival, measured in the short term, doesn’t necessarily predict longer life. And as the new study shows, it may also fail to predict better quality of life.

“In cancer patients there are two important things when evaluating a therapy: whether it extends survival and whether it improves quality of life (even if it doesn’t extend survival),” Xie explained.

Although many studies have measured progression-free survival, most have not reported on health-related quality of life. Xie and his colleagues were able to find 38 studies, including a total of 13,979 cancer patients with 12 different cancer types, that did look at both endpoints.

Data pooled from all 38 studies showed no significant association between progression-free survival and quality of life.

The researchers had difficulty comparing data from the studies because quality of life was not always measured in the same way. Xie hopes that in the future, researchers will standardize the way they measure quality of life.

Dr. Robert Ferris, director of the Hillman Cancer Center at the University of Pittsburgh Medical Center, isn’t ready to throw out progression-free survival as an indicator of a cancer drug’s effectiveness. But the early marker may under- or over-estimate the worth of a medication, Ferris said in a phone interview.

“Early response doesn’t always predict long term survival,” said Ferris, who is not affiliated with the new research. “For example, immunotherapy drugs are known for their long-term benefits but may not have early rapid shrinkage of a tumor.”

Also, Ferris said, measuring quality of life can be tricky. “Everybody sees it differently,” he explained. “Some might see it as a reduction in pain. Others might see it as the ability to interact socially or the ability to swallow or the ability to get out of bed. Others might see it as a reduction in fatigue.”

Still, progression-free survival can be used as an early indicator that researchers are on the right track with a new drug, Ferris said. When an experimental drug does a good job of controlling a tumor, for example, that might give researchers the impetus to conduct larger-scale trials.

“You have to be judicious in how you use it,” Ferris concluded.

SOURCE: bit.ly/2QoLsZv JAMA Internal Medicine, online October 1, 2018.