IN OCTOBER 1854, a government entomologist was inspecting some farmland outside the town of Ottawa, in northern Illinois, when he came upon a disturbing scene in a cabbage patch.
THE LARGE OUTER leaves of the vegetables were “literally riddled with holes, more than half their substance being eaten away.” With each step he took around the ravaged cabbages, tiny swarms of little ash-gray moths rose from the ground and flitted away. This was, it appears, the first record in the United States of the diamondback moth, an invasive pest that in its larval form shows a fondness for cruciferous vegetables. By the late 1800s the moths were chewing through the leaves of cabbages, brussels sprouts, collards, and kale from Florida to Colorado.
To fight this invasion, farmers started bombarding their fields with primitive pesticides. This worked. Or seemed to. It killed most of the moths, but those that survived the poison reproduced, and the population bounced back stronger than ever. For decades, one pesticide after another failed as the moths evolved to withstand it. Even the grievously toxic DDT was no match for the diamondback. Beginning in the late 1950s, agriculture experts started to abandon the idea of eradication and adopted a new strategy. Farmers would leave the moths alone until their numbers exceeded a certain threshold, and only then would they deploy pesticides. Remarkably, this helped. The moths did not die out, but the pest could be managed and crop damage held in check.
When Robert Gatenby heard this history of the diamondback moth in 2008, he immediately latched onto it. Gatenby is not a farmer nor an agronomist nor a fan of cruciferous vegetables—in fact, he deeply loathes brussels sprouts. He is a radiologist by training and heads the radiology department at the H. Lee Moffitt Cancer Center in Tampa, Florida. But unlike your typical doctor, he is also obsessed with the evolutionary principles put forth more than 150 years ago by Charles Darwin. The story of the diamondback moth appealed to Gatenby as a useful metaphor for his own project—one concerned not with crops but with cancer
Like the diamondback moth, cancer cells develop resistance to the powerful chemicals deployed to destroy them. Even if cancer therapies kill most of the cells they target, a small subset can survive, largely thanks to genetic changes that render them resistant. In advanced-stage cancer, it’s generally a matter of when, not if, the pugnacious surviving cells will become an unstoppable force. Gatenby thought this deadly outcome might be prevented. His idea was to expose a tumor to medication intermittently, rather than in a constant assault, thereby reducing the pressure on its cells to evolve resistance.
Just as ecologists allow for a manageable population of diamondback moths to exist, Gatenby’s method would permit cancer to remain in the body as long as it doesn’t spread further. To test this idea, Gatenby got permission in 2014 to run a trial on advanced-stage prostate cancer patients at Moffitt. The patients had cancer that no longer responded to treatment; their drug-resistant cells were winning an evolutionary battle within the body, surviving an onslaught of toxic drugs where weaker cancerous cells had succumbed. The hope was that, by using a precise drug-dosing scheme developed using evolutionary principles, they could slow the rise of the mutations that would endow some cancer cells with the fitness to survive. Gatenby’s name for the approach was adaptive therapy.One of the patients in the trial was Robert Butler, a British oil-exploration engineer who had retired in Tampa. In 2007 he was diagnosed with prostate cancer, and seven years later, after taking the drug Lupron and getting blasts of radiation, his prostate tumor had progressed to stage 4, advanced cancer. Butler did not give up, though. He tried a newly approved immunotherapy treatment—one that involved having cells from his blood sent by courier to a facility outside Atlanta, where they were mixed with a molecule that activates immune cells, and then shipped back to Florida to be injected back into him. The treatment was expensive—its sticker price can be as high as $120,000—but the threat that the cancer would progress remained.
When Butler and his wife showed up at his oncologist’s office at the Moffitt Cancer Center in August 2014, they braced for what would come next; they had heard about invasive treatments, like radioactive seed implants. So they were intrigued when the doctor told them about Gatenby’s trial and asked if Butler wanted to participate. He would take a powerful and exceedingly expensive drug called Zytiga, but not in the scorched-earth, kill-all-the-cells fashion that is standard. Instead he would receive only as much Zytiga as was necessary to stop the cancer from growing. The idea was radical and counterintuitive. His last best shot at escaping death from his cancer was to give up on curing it.
Knowing the modified Zytiga regimen wasn’t designed to rid him of cancer left Butler, the engineer, with a question about how the doctors would measure the success of their new treatment approach. He asked, “How do we know this stuff is working?” And one of his doctors replied, “Well, you won’t be dead.”
IN THE UNITED States we use military metaphors when we talk about cancer. We battle and we fight, and if we survive, we’re victorious. The attitude traces back in part to 1969, when the Citizens Committee for the Conquest of Cancer ran an ad in The Washington Post and The New York Timesimploring the president with the words “Mr. Nixon: You can cure cancer.” The call to action helped trigger the country’s “war on cancer” with a determination that, using enough medical weaponry, the malignant foe could be obliterated.By the mid-1970s, however, signs were beginning to emerge that certain strategies aimed at total eradication were liable to backfire. Against this backdrop, a cancer researcher named Peter Nowell published a seminal paper in Science in 1976. Nowell conjectured that evolutionary forces drive certain cell populations in tumors to become progressively more malignant over time. The cells inside a tumor are in competition, not only with nearby healthy cells, Nowell argued, but also with each other. Nowell suggested—and later research confirmed—that certain DNA alterations grant cancer cells resistance against chemotherapy or other treatments, causing them to edge out drug-sensitive cells through a process of natural selection.
Nowell conveyed his ideas to his students at the University of Pennsylvania School of Medicine, sometimes smoking a cigarette as he lectured. His theories were respected but slow to catch on. He emphasized that tumors may become deadlier as they accumulate more genetic errors. It was an idea ahead of its time. Scientists back then didn’t have the technical capability to measure all the changes in the vast genomes of tumor cells. Instead, they could sequence only little tidbits of DNA at a time, and most scientists viewed cancers as the fruit of just a few genetic mutations.
One of the medical students listening to Nowell lecture in the late 1970s happened to be a young Bob Gatenby. But Nowell’s ideas didn’t make a strong impression on him, Gatenby says; instead, what inspired him was what he witnessed in his first years as a practicing radiologist on the bloody front lines of the war on cancer.
By the mid-1980s, Gatenby had secured a job at the Fox Chase Cancer Center in Philadelphia. At that hospital and others around the country, clinical trials were putting breast cancer patients through an extreme treatment: a combination of a potentially lethal dose of chemotherapy followed by a bone marrow transplant. The treatment was harrowing. The women had diarrhea and nausea, and some had so much lung damage they had difficulty breathing. Others experienced liver damage and weakened immune systems that left them vulnerable to serious infections. As a radiologist, Gatenby’s job was to interpret x-rays and other scans of the patients, and he saw the treatment failing. Out of more than 30,000 women with breast cancer in the US who underwent the procedure between 1985 and 1998, as many as 15 percent died from the treatment itself. “What happened was these women suffered horribly, and they weren’t cured,” Gatenby says.
Around the same time as the breast cancer trials, the father of a colleague of Gatenby’s came to the hospital to receive an initial, aggressive round of chemotherapy for lung cancer. According to the colleague, her father arrived on a Friday with no apparent symptoms and was dead by Monday. “That event to me was very traumatizing,” Gatenby recalls, and the cause to him seemed obvious. “I couldn’t understand why you would treat someone with a fatal disease and kill them with your therapy. It just didn’t feel right to me.” During this fraught period, Gatenby’s own father died from esophageal cancer.
Gatenby felt there must be a better way to treat cancer—to outsmart it rather than carpet-bomb it. He had studied physics in college and believed that biologists could leverage equations to capture the forces driving cancer the same way physicists use math to describe phenomena like gravity. Whereas Nowell had put forth general theories about how cancers followed evolutionary principles, Gatenby was taking a further leap: He wanted to figure out a way to describe the evolution of cancers with mathematical formulas.