The surprisingly high rate reveals not just the scope and cost of wasted opportunities that deprive patients of potential advances, but also the extent of barriers such as money, logistics and even the mistaken fear that people won't get the best care if they join one of these experiments.
"Clinical trials are the cornerstone of progress in cancer care," the way that new treatments prove their worth, said Dr. Matthew Galsky of the Icahn School of Medicine at Mount Sinai Hospital in New York.
When an experimental drug or other treatment fails to make it to the market, people often think it didn't work or had too many side effects, but the inability to complete studies can doom a drug, too, Galsky said.
He helped lead an analysis of 7,776 experiments registered on Clinicaltrials.gov, a government web site for tracking medical experiments, from September 2005 to November 2011. All were mid- or late-stage studies testing treatments for various types of cancer in adults.
About 20 percent of the studies were not completed for reasons that had nothing to do with the treatment's safety or effectiveness (legitimate reasons for ending a study early).
Company-sponsored studies were less likely to be completed than those sponsored by the government or others. Late-stage cancer trials can cost companies "tens to even hundreds of millions of dollars," and that money is wasted if no clear answer on the drug's value is gained, said Dr. Charles J. Ryan, a cancer specialist at the University of California, San Francisco.
He heads the program for a conference later this week in San Francisco where Galsky's study will be presented. It was discussed Tuesday in a telebriefing by the American Society of Clinical Oncology, an organization for doctors who treat cancer.
Ryan and Galsky said they hoped the study would spur more research on why more patients don't participate. In most cases, the treatment being tested is provided for free, but there can be other costs such as lab tests. Some states require insurers to cover these additional costs, but others do not, so money may be one hurdle for patients.
Some doctors do not strongly encourage patients to participate in studies, and sometimes patients fear they'll get a dummy treatment instead of real medicine. However, in cancer clinical trials, ethical standards require that all patients get the current best care, plus a chance at an experimental treatment.
"Patients still have concerns about getting a placebo, but they're always going to get at a minimum the standard of care," said Shelley Fuld Nasso, head of the National Coalition for Cancer Survivorship, a patient advocacy and education organization.
Doctors need to encourage more patients to participate, and clinical trial designers need to make sure they are testing key questions and treatments to honor the contributions of study participants, she said.
Cancer patient info: http://www.cancer.net
Decision-making guide: http://bit.ly/L67zkT
Clinical trials: http://www.clinicaltrials.gov
Marilynn Marchione can be followed at http://twitter.com/MMarchioneAP