Taking new aim at cancer

You may have heard that former President Jimmy Carter’s melanoma, which had previously metastasized to his brain, has vanished. This news has cast light on a type of cancer treatment called immunotherapy, which helps the body’s own immune system fight cancer cells.

The drug used for President Carter, pembrolizumab (Keytruda), is designed to block a cellular pathway known as PD-1, which hinders the immune system’s ability to attack melanoma cells. It was approved last year by the FDA and, so far, has proven to be successful in melanoma and other cancers. In clinical trials, tumors shrank in more than 30% of people who received the drug.

President Carter also received radiation as part of his treatment (along with surgery to remove cancer that had spread to his liver). So it is difficult to say if pembrolizumab alone wiped out the tumors in his brain, or if it was the combination of the two treatments, says Dr. Patrick Ott, clinical director of both the Melanoma Center and the Center for Immuno-Oncology at Harvard-affiliated Dana-Farber Cancer Institute. Though pembrolizumab has been tested for treating melanoma, it has not yet been formally studied for the treatment of melanoma that has metastasized to the brain.

“Melanoma in the brain is the hardest to treat. Most cancer drugs do not work in the brain to the same extent as other parts of the body because the brain has a barrier that prevents drugs from reaching it. So in this way, this type of treatment is quite promising,” says Dr. Ott.

The pros and cons of targeted therapies

Immunotherapy is often included in a group of cancer treatments called targeted therapy. These treatments work in different ways to either block a tumor’s blood supply, kill cancer cells directly, trigger the cancer cell death process, or, as in the case of immunotherapy, boost your immune system to attack cancer cells.

The kind of drug a person gets depends on his or her individual cancer and its stage (how far it has spread). Treatment is often given one to two times a day for three months to a year.

Targeted therapy has advantages over chemotherapy. For example, chemotherapy attacks cancer cells, but also damages nearby healthy cells in the process. It is like hosing down a large area of a yard just to water a tree.

In comparison, targeted therapy focuses on the cancer cells’ inner workings — the programming that sets them apart from normal cells. This way, surrounding healthy cells are often spared, and the result is more attention given to the cancer cells, with less severe side effects.

Targeted therapies do have their limits. For one, they do not work for everyone, or for every kind of cancer. For instance, right now, only about 10% of people with lung cancer are candidates for targeted therapy. This is because current targeted therapy focuses on a mutation that is found in only 10% of lung cancers.

Cancer cells also can become resistant to targeted therapy, either because the original target changes through mutation, the tumor finds a new pathway to grow, or both. “This is why therapies often work best in combination — either with other targeted therapies or one or more traditional chemotherapy drugs,” says Dr. Bruce Johnson, professor of medicine at Harvard Medical School.

Still, these targeted therapies may offer better options for certain cancer patients. “These are not miracle treatments,” says Dr. Ott. “But they can have good outcomes in the right situation.”