Reports relating to two clinical trials presented at the recent American Society of Clinical Oncology conference in Chicago raised hopes for cancer treatment breakthroughs. One trial focused on activating the body's immune system to combat cancers, the other on targeting tumors directly.
Using the Immune System to Fight Cancer
At the conference, two experimental drugs of the class known as immune checkpoint inhibitors were reported to have significantly shrunk tumors in some patients with advanced skin, lung or kidney cancer, by enabling the body's immune system to recognize and attack the cancer cells. A number of companies are working to develop such "immunotherapies," but the drugs in the new study were developed by Bristol-Myers Squibb. Although the treatments proved beneficial for only a minority of the more than 500 advanced-stage cancer patients who participated in the trial, the results are considered a major success because the degree of tumor shrinkage exceeded expectations.
Currently, only one immune checkpoint inhibitor has been approved by the Food and Drug Administration for the treatment of cancer — Yervoy from Bristol-Myers Squibb, whose clinical trials pleased oncologists with a 20 percent success rate in delivering long-term survival to patients with advanced melanoma. Some patients who would have been expected to die within a few months have lived for several years on the drug.
Immunotherapies may be the future of cancer treatments, but there can be side effects. They can include diarrhea or inflammation of the colon, which are associated with increased immune system response. The immune system, once activated, can potentially attack healthy tissue. But "the side effects for traditional chemotherapy are often much worse," says oncologist James L. Gulley, deputy chief of the Laboratory of Tumor Immunology and Biology at the National Cancer Institute and director of the lab's Clinical Trials Group. (His office was not involved in the recent clinical trial.)
Patients who experienced such side effects in the recent immunotherapy clinical trial were treated with steroids, and, Gulley says, "What is encouraging is that in general the antibodies were well tolerated … and the response was maintained long term. As an early signal, it's quite hopeful."
Gulley says that the hope in the immunology field is that the new drugs can be combined with other immunotherapies, including vaccines, to create better outcomes than have so far been seen through the use of one drug alone. "I think eventually we're going to find that attacking the tumor on many fronts may be better than attacking it on one front at a time," he says.
Such treatments, however, are a number of years away from FDA approval. The success or failure of upcoming larger-scale trials will determine their future.
A 'Guided Missile' Attack on Breast Cancer
The other study presented at the oncologists' conference related to clinical trial results for T-DM1, a very different type of cancer drug that some experts are calling a "guided missile." It was developed by Genentech to deliver a poison payload of toxic antibodies directly to cancer cells in breast cancer patients. Since the antibodies are not activated until they reach the tumor, side effects are limited. Twenty-five such drugs are now in various stages of clinical trials. The FDA will consider T-DM1 for approval in breast cancer patients later this year, and if the agency signs off, it could become widely available sometime in 2013, making it the first such drug on the market for treatment of a common type of cancer.
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In the recent clinical trial, about 85 percent of patients treated with T-DM1 were still alive after one year, compared to 77 percent in a control group of patients who were treated with Xeloma and Tykerb, two drugs now commonly used to treat breast cancer. Also, about 41 percent of the women treated with T-DM1 experienced serious side effects, as opposed to 57 percent of those in the control group. All of the women in trial had the form of breast cancer known as HER-2 positive. About 20 percent of all breast cancer patients are of this type. Their tumors have a high level of the protein HER-2, which T-DM1 is specifically designed to attack.
Experts found the T-DM1 results especially encouraging because even patients who did not significantly outlive the control group showed more improvement than the control group over the course of the treatment. "It's less toxic … and also more effective," Dr. Clifford Hudis of Memorial Sloan-Kettering Cancer Center told The New York Times. "How often do we get that?"