Scientists, physicians and researchers must always be cautious when they talk about new findings. Even the most exciting therapies can have weaknesses and downsides, and it’s important to point them out.
That’s true with immunotherapy, which does have limitations. But its successes are remarkable, and it is now recognized as a game changer in the field of cancer treatment.
Harnessing the immune system
Our immune systems send specialized cells to fight infection from viruses, bacteria and other agents. These cells even stop some cancers from taking hold. But cancer can often evade the immune system by hiding from it or disrupting its function.
Immunotherapy uses several strategies to reset the immune response so it can attack cancer cells. Research is focusing on these treatments:
• Checkpoint inhibitors. The cells that fight infection are called killer T-cells. They are so powerful that they have mechanisms — called checkpoints — to keep them from attacking normal tissue. Cancer takes advantage of these checkpoints to turn off the immune system.
Researchers have developed medicines called checkpoint inhibitors to block checkpoints altogether, stopping cancer from using them to evade the immune system. Several checkpoint inhibitors have been approved by the FDA, including Keytruda, Opdivo, Tecentriq and Yervoy. Initially these drugs were used after standard chemotherapy had stopped working, but they may soon be approved as first treatments.
These drugs have been very successful in treating melanoma skin cancer, which previously had no effective treatment. Up to 60 percent of melanoma patients respond well to checkpoint inhibitors, and some patients have gone more than five years with no recurrence of their cancer. Former president Jimmy Carter is a good example — the melanoma that spread to his brain essentially disappeared after treatment with Keytruda.
Checkpoint inhibitors are also used for Hodgkin’s lymphoma and cancers of the bladder, lung, liver, kidney, and head and neck cancer.
• Cell therapies. Also called adoptive cell transfer, these treatments work by engineering cells from the person’s own immune system to attack cancer cells. Killer T-cells are collected from the person’s blood and then modified to recognize a specific protein on the cancer cells in his or her body. These modified cells are called CAR-T cells, and when they are infused back into the patient they multiply and kill the cancer.
This form of immunotherapy has worked very well against deadly forms of leukemia and lymphoma. Clinical trials have shown that in many cases, all signs of the cancer disappear and the subjects remain in remission for extended periods. CAR-T cells are also being studied for use against other types of cancer.
Cell therapy is difficult to accomplish because it must be personalized for each patient. It’s still experimental and as yet no specific cell therapies have been approved by the FDA.
• Cancer vaccines. Unlike most vaccines, these medicines aren’t meant to prevent a disease. Instead, they trigger the immune system to strengthen its response to an existing cancer. This happens when an inactivated form of the cancer cells, or parts of these cells, are introduced into the body to trigger an immune response against them. Cancer vaccines can delay or stop the growth of the cancer, shrink tumors or prevent cancer from returning.
A vaccine called Provenge has been approved by the FDA for use against advanced prostate cancer, and researchers are working on other vaccines. However, vaccines have not yet shown the significant promise of other immunotherapies.
Immunotherapy treatments are often used in conjunction with standard chemotherapy or radiation therapy. In fact, there is evidence that using a type of radiation therapy called SBRT at one site can increase the effectiveness of some immunotherapy at multiple sites.
Immunotherapies do have some drawbacks. They don’t work for everyone, so while some people see their cancer drastically reduced or even disappear, others have no response to treatment. Also, some immunotherapies can take weeks or months to begin working.
Side effects can also be a problem. Since boosting the immune system releases it against healthy cells as well as cancer cells, conditions such as rheumatoid arthritis, immune colitis and thyroid disease can develop. Other side effects include high fever and low blood pressure. In severe cases people may need to temporarily stop or alter their treatments.
However, these side effects occur in a small minority of people and they can usually be relieved with steroid medicines or other treatments. People who have previously had chemotherapy or radiation therapy notice a significant difference with immunotherapy — issues such as nausea and hair loss that are typically associated with those treatments do not occur and they may have no side effects at all.
The advances that led to these new therapies came after many years of basic research into how the immune system works. But now that science has uncovered these pathways the process is moving quickly. FDA approval of new immunotherapies is happening much faster than in the past, with therapies reaching the market in months instead of years.
This progress is cause for excitement among physicians and patients alike. Cancer doctors now have new ways of treating, monitoring and interacting with patients who are receiving these treatments. And many patients have a better chance at living well with cancer for years, or even being cancer free.
You can learn more about immunotherapy for cancer by visiting the American Cancer Society at www.cancer.org.