To secure F.D.A. approval, after patenting a drug, drug companies race the clock to show that their product is safe and effective. The more quickly they can complete those studies, the longer they have until the patent runs out, which is the period of time during which profit margins are highest. Developing drugs to treat late-stage disease is usually much faster than developing drugs to treat early-stage disease or prevention, because late-stage disease is aggressive and progresses rapidly. This allows companies to see results in clinical trials more quickly, even if those results are only small improvements in survival.

This very lesson is taught in some medicinal chemistry textbooks. For instance, one notes that “some compounds are never developed [into drugs] because the patent protected production time available to recoup the cost of development is too short.”

The clinical trials necessary for the F.D.A. to approve drugs for commercialization take years. Though a patent lasts 20 years (before any extensions), a typical drug comes to market with about 12.5 years of patent life remaining. But would-be innovators have some control over the length of time between receipt of a patent and F.D.A. approval — the “commercialization lag.” By studying patients in whom safety and efficacy can be demonstrated more quickly, innovators can reduce this lag. (Recent studies suggest that commercialization lag times may be decreasing for some types of drugs.)

Many more cancer trials focused on treatments for patients with late-stage cancers than for early-stage cancers, according to the study. Between 1973 and 2011, there were about 12,000 trials for relatively later-stage patients with a 90 percent chance of dying in five years. But there were only about 6,000 focused on earlier-stage patients with a 30 percent chance of dying. And there were over 17,000 trials of patients with the lowest chance of survival (those with recurrent cancers) but only 500 for cancer prevention, which confer the longest survival gains. The bias toward studies focused on patients with shorter survival duration is more prevalent among privately financed trials than for publicly financed ones.

Ms. Williams’s study estimated that the commercialization lag’s incentive to invest in drugs of shorter duration benefit led to 890,000 lost life-years among American patients found to have cancer in 2003 alone.