Do cancer treatment vaccines really work?
Vaccines aren't only for prevention. When it comes to cancer, some are supposed to treat tumors that have already started. This seems like a great idea—the vaccines get your own immune system to fight the tumor—but they don't have a great reputation. The reason: When they have been tested on cancer patients, the number who benefit turns out to be surprisingly low. In fact, a paper in the journal Nature Medicine examined a bunch of trials and found the best response rates were on the order of 2 to 3 percent, which is pretty measly.
But a number of cancer researchers are now arguing that the problem isn't in the vaccines—it's in the way they've been tested.
New cancer drugs are often tested on people who have already tried older drugs and failed to improve. There's a certain logic to that. If patients were getting better on the old drugs, there'd be no reason to try something new. If it ain't broke, don't fix it. In fact, it'd be cruel to take someone off a drug that's helping them and ask them to try an experimental drug that may not help at all.
But that's a problem for cancer vaccines. Remember, they boost the immune system. Yet if they are tested on patients who have already tried lots of anticancer drugs, chances are the immune system is seriously damaged. So there is not much of an immune system left to boost. Chemotherapy, for instance, kills healthy cells along with cancer cells, and that includes immune cells.
"These trials may be doomed to fail," says Jeffrey Schlom, an immunologist at the National Cancer Institute and a leading vaccine researcher.
So the National Cancer Institute is beginning to test vaccines in a new way, in people in earlier stages of cancer who haven't been through the chemotherapy wringer. The test subjects are men with prostate cancer and rising prostate-specific antigen (PSA) levels but no other sign that their cancer has spread. Some small tests have been encouraging.
But Schlom is quick to add that early trials aren't real proof.
"We haven't shown anything yet" because these have been tests on small groups of men, without any other group with which to compare them. The good results could be due to chance. So the cancer institute is beginning new tests with larger groups of men, who will be compared against a matched group whose members don't get the vaccine.
It's a new way of evaluating a new type of medicine. And it might spawn a new way to treat an old and deadly disease.