Pten activity is somewhat impaired in the vast majority of human cancers. A drug that reactivates the gene could help curb cancer growth.

Dr. Mustafa Sahin, an expert on the Pten gene at Boston Children’s Hospital, called the new research a “tour de force study.” The result is “a paradigm shift in the field and very exciting in terms of its therapeutic implications,” Dr. Sahin, who was not involved in the research, wrote in an email.

Dr. Pier Paolo Pandolfi, senior author of the paper and director of the cancer center at Beth Israel Deaconess Medical Center in Boston, has spent years trying to find a way to restore Pten activity.

The gene governs production of an enzyme that stops cells from dividing too quickly, reducing the chances that cancers will form. With reduced activity in Pten, cells grow uncontrollably .

Pten mutations do not completely halt the gene’s functions . Instead, the mutations tamp down the gene’s activity, so cells make less of the enzyme needed for orderly growth.

But one of the hardest things for researchers to do is to find a way to increase, rather than turn off, a gene’s activity. Eventually, Dr. Pandolfi and his colleagues learned enough about the Pten system to reason that i3c might do the trick.

“We got lucky, or smart,” he said.

Dr. Pandolfi and his colleagues tested their treatment on human prostate cancer cells and in mice bred to develop prostate cancer. It worked: In the cells and in mice, i3c treatment resulted in fewer cancers, and those that arose were small and less deadly.