Clinical trials testing new types of cancer treatments are having difficulty enrolling enough participants, and it can be hard to tell which patients might be the best candidates for particular drugs, according to a report in the New York Times.
There are currently more than 1,000 cancer immunotherapy trials under way. Instead of killing off fast-growing cells the way traditional chemotherapy does, immunotherapy helps the immune system recognize and attack cancers. Targeted therapy, another new approach, homes in on cancers with specific genetic characteristics. Although some of these new treatments are highly effective, they work only for a subset of patients.
Some targeted therapies work against cancer mutations that are very rare, and finding enough patients who have them requires expensive genetic screening of a large number of people. For some immunotherapies, researchers do not yet understand what characteristics to look for to predict whether a treatment is likely to work.
The small number of people eligible for trials, and the large number of drugs being tested as pharmaceutical companies try to penetrate this lucrative new market, have created a logjam, according to the Times. Some experts have suggested that drug companies are testing too many similar types of drugs, such as PD-1 checkpoint inhibitors, instead of addressing new research questions.
Companies may have to spend a great deal of time and money conducting international searches for the subset of patients likely to benefit from their new therapies. For example, GlaxoSmithKline searched for 13 months in the United States, Asia and Europe to find 59 patients with a rare lung cancer mutation targeted by an experimental two-drug combo.
Because most cancer patients are treated outside of academic medical centers, they may never even be evaluated for clinical trial eligibility. To test a drug that targets a mutation found in only 1 percent of cancer patients, researchers at Memorial Sloan Kettering offered to pay for genetic testing of patients at community medical centers in three states.
Clinical trials with too few participants can have a hard time showing conclusively that a drug candidate works and that its effects are not just the result of chance, which makes it less likely that the drug will be approved by the Food and Drug Administration and covered by insurers. In addition, studies with few patients may fail to reveal uncommon side effects.
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