For more than a century, researchers were puzzled by the uncanny ability of cancer cells to evade the immune system. They knew cancer cells were grotesquely abnormal and should be killed by white blood cells. In the laboratory, in Petri dishes, white blood cells could go on the attack against cancer cells. Why, then, could cancers survive in the body?
The answer, when it finally came in recent years, arrived with a bonus: a way to thwart a cancer’s strategy. Researchers discovered that cancers wrap themselves in an invisible protective shield. And they learned that they could break into that shield with the right drugs.
When the immune system is free to attack, cancers can shrink and stop growing or even disappear in lucky patients with the best responses. It may not matter which type of cancer a person has. What matters is letting the immune system do its job.
So far, the drugs have been tested and found to help patients with melanoma, kidney and lung cancer. In preliminary studies, they also appear to be effective in breast cancer, ovarian cancer and cancers of the colon, stomach, head and neck, but not the prostate.
It is still early, of course, and questions remain. Why do only some patients respond to the new immunotherapies? Can these responses be predicted? Once beaten back by the immune system, how long do cancers remain at bay?
Still, researchers think they are seeing the start of a new era in cancer medicine.
“Amazing,” said Dr. Drew Pardoll, the immunotherapy research director at Johns Hopkins School of Medicine. This period will be viewed as an inflection point, he said, a moment in medical history when everything changed.
Researchers and companies say they are only beginning to explore the new immunotherapies and develop others to attack cancers, like prostate, that seem to use different molecules to evade immune attacks. They are at the earliest stages of combining immunotherapies with other treatments in a bid to improve results.
“I want to be very careful that we do not overhype and raise patients’ expectations so high that we can never meet them,” said Dr. Alise Reicin, a vice president at Merck for research and development.
But the companies have an incentive to speed development of the drugs. They are expected to be expensive, and the demand huge. Delays of even a few months mean a huge loss of potential income.
The story of the new cancer treatments started with the discovery of how cancers evade attacks. It turned out that they use the body’s own brakes, which normally shut down the immune system after it has done its job killing virus-infected cells.
One braking system, for example, uses a molecule, PD-1, on the surface of T-cells of the immune system. If a target cell has molecules known as PD-L1 or PD-L2 on its surface, the T-cell cannot attack it.
So some cancer cells drape themselves in those molecules. The effect, when T-cells are near, is like turning off a light switch. The T-cells just shut down.
Cancers that do not use PD-L1 or PD-L2 are thought to use other similar systems, just starting to be explored. Body systems have a lot of redundancy to tamp down immune attacks. But for now, the PD system showed researchers how cancer cells can evade destruction.
“That is what has been realized in the past few years,” said Ira Mellman, vice president of research oncology at Genentech. “Tumor cells are making use of this brake.”
The discovery led to an idea: Perhaps a drug that covered up any of those PD molecules, on the cancer cells or on white blood cells would allow the immune system to do its job.
The first indication that a cancer’s protective shield might be breached came in 2010, after a trial of the drug ipilimumab in patients with otherwise untreatable melanoma. The drug unleashes the immune system, letting it overwhelm tumors even if they have a protective shield.
Patients who took the drug survived an average of 10 months, or four months longer than those randomly assigned to a different treatment. And about 20 percent of patients who responded have now survived up to 10 years. It was the first drug to improve survival for patients with metastatic melanoma in a randomized trial.
“It was spectacular,” said Dr. Axel Hoos, vice president for oncology research and development at GlaxoSmithKline, who helped develop the drug when he was at Bristol-Myers Squibb. “Until that tipping point, immunotherapy had a bad name. It didn’t work.”
The drug was approved for melanoma in March 2011, with a high price tag — $120,000 for a course of therapy.
It had another drawback. By unleashing the immune system, it sometimes led to attacks on normal cells. In some cases, the reaction was fatal. But the trial was a proof of concept. It showed that cancers can succumb to an attack by the immune system.
Emblems of hope
As researchers continue to study the new drugs and ask if they can improve their results by combining them with other therapies, they are heartened by some of the rare patients whose cancers were halted by the drugs. They caution that these patients are unusual; critical studies to reveal the drugs’ effects on populations of cancer patients are still underway.
“What you really want to know,” said Dr. Roger Perlmutter, the president of Merck Research Laboratories, “is, are people living longer?” For that, “you just have to wait,” he continued, adding, “What I don’t want to do is give people false hope.”
But some patients, like two treated at Hopkins, have become emblems of hope.
In 2007, Dennis Sisolak, who is 72 and a retired engineer from Bel Air, Md., learned he had kidney cancer. The tumor was huge, and the cancer had spread. After he tried two new drugs to no avail, his doctor, Dr. Charles Drake, a kidney cancer specialist at Johns Hopkins, enrolled him in an early phase clinical trial of a PD-1 inhibitor. His cancer disappeared on scans and has not returned, even though he has had no treatment for a year.
“I have a lot of people praying for me,” Sisolak said.
The recent discovery that cancers can evade the immune system by wrapping themselves in a protective shield offered a bonus: a way to try to thwart their growth.
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