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When Evidence Says No, But Doctors Say Yes

By ProPublica  
   February 22, 2017

In 2010, on the strength of a crossover trial, Provenge became the first cancer vaccine approved by the FDA. A cancer vaccine is a form of immunotherapy, in which a patient's own immune system is spurred by a drug to attack cancer cells. Given the extraordinary difficulty of treating metastatic cancer, and high expectations following the abject failure of other cancer vaccines, the approval of Provenge was greeted with ecstatic enthusiasm. One scientific paper heralded it as "the gateway to an exciting new paradigm." Except, Provenge did not hinder tumor growth at all, and it's hard to know if it really works.

Provenge was approved based on the "IMPACT study," a randomized, placebo-controlled trial initially meant to see whether Provenge could stop prostate cancer from progressing. It didn't. Three-and-a-half months into the study, the cancers of patients who had received Provenge and those who had received a placebo had advanced similarly. Nonetheless, patients who received Provenge ultimately had a median survival time of about four months longer than those who received the placebo. Due to the way in which the IMPACT trial unfolded, however, it's hard to tell if Provenge was truly responsible for the life extension.

Because Provenge did not halt tumor growth, many of the patients who began the study on it also started to receive docetaxel, a chemotherapy drug that is well established to treat advanced prostate cancer. The cancers of the patients on a placebo were also progressing, so they were "crossed over" and given Provenge after a delay. Their cancer continued progressing, and after another delay, many of them also got docetaxel. In the end, fewer patients in the group that started on a placebo received docetaxel, and, when they did, they got it later in the study. So Provenge may have worked, but it's impossible to tell for sure: Was the slightly longer survival of one group because they got Provenge earlier or because the other group got docetaxel later?

ProPublica is an independent, non-profit newsroom that produces investigative journalism in the public interest.


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