These medicines harness the body's immune system to combat certain cancers.

Your immune system—amped up. That’s the power of immunotherapy.

So, what exactly is immunotherapy? It’s a category of medicine that works differently than traditional cancer treatments. Instead of attacking cancer directly, immunotherapy activates the body’s immune system to carry out the assault.

Think of it this way: Your immune system is like an armed militia fending off germs and disease. It’s effective, but not foolproof. Sometimes troublemaking cells develop, grow, and spread in the body without being detected or annihilated. Cancer immunotherapy enhances the immune system’s search-and-destroy capabilities.

“It’s arming the soldiers with better defenses and better weapons to kill the enemy,” says Michael Caligiuri, MD, immediate past president of the American Association for Cancer Research (AACR) and president and physician-in-chief of City of Hope National Medical Center in Duarte, California.

Some people call immunotherapy the “fifth pillar” in cancer treatment, after surgery, radiation, chemotherapy, and targeted therapy. It’s often delivered after, or in combination with, traditional cancer therapies. But it doesn’t work for everyone. And, in some cases, the drug stops working and the cancer recurs.

Always discuss the benefits and risks of immunotherapy with your oncology team.

How does immunotherapy for cancer work?

Normally, your immune system wages war on germs and other bad actors that cause illness and disease. But cancer has ways of hacking the system. Here are two common ploys:

  • It disarms the immune system. “Cancers have learned how to put the immune system to sleep—just like delivering anesthesia,” explains Dr. Caligiuri, who conducts research in immunology, leukemia, and lymphoma. “That allows the tumor to grow unchecked or uninhibited.”
  • It hides in plain sight. Foreign substances called antigens typically sit on the surface of tumors. Antigens are like flags alerting the immune system that danger is present, so rev up and attack! But sometimes a rogue cell fails to express that antigen and, if there’s no flag, “the immune system won’t see it,” he says.

Each cancer immunotherapy works in a different way to help your immune system defeat the disease. Some medicines make it easier for the immune system to recognize and respond to cancer. Others boost the immune system’s ability to fight cancer.

Types of immunotherapy

Here are the main types of immunotherapy used for cancer treatment. It is not a comprehensive list. Your oncologist can tell you about other approved or experimental treatments.

CAR T-cell therapy
This type of treatment uses a person’s own immune cells to fight cancer.

Here’s how it works: Some T cells (disease-fighting white blood cells) are extracted from a patient’s blood. In the lab, scientists reengineer the cells. A “receptor” that recognizes the cancer’s antigen, or flag, is inserted. A large supply of these altered cells is grown and given back to the patient through an IV.

CAR T cells “act like magnets for cancer cells,” according to the American Cancer Society (ACS). This type of immunotherapy is used to treat certain patients with specific types of leukemia and lymphoma.

Checkpoint inhibitors
These drugs prevent cancer cells from using “immune checkpoints”—proteins that regulate your immune response—to escape attack.

Checkpoints are meant to prevent your immune system from assaulting normal, healthy cells. Cancer games this system by slamming the breaks on your immune response. It puts your T cells on “standby mode,” says the ACS. Or, as Dr. Caligiuri explains it, cancer puts your immune response to sleep.

Checkpoint inhibitors are the antidote. These drugs wake up sleeping T cells, unleashing the power of the immune system against the cancer.

You might be given a checkpoint inhibitor if you have melanoma; lymphoma; or bladder, kidney, or lung cancer.

Monoclonal antibodies
These are proteins made in a lab. They can be used as immunotherapy to target antigens on cancer cells. This type of therapy can help the immune system “find and destroy” these cells, explains Cancer.Net, the patient information website of the American Society of Clinical Oncology (ASCO).

The drug rituximab is a classic example of a monoclonal antibody that works as immunotherapy in the treatment of lymphoma, says ASCO expert Michael Sabel, MD, chief of the division of surgical oncology at the University of Michigan in Ann Arbor.

There are two types of cancer-related vaccines: those that prevent infections that can lead to cancer and those that treat cancer once you have it.

Vaccination against the human papillomavirus, for example, can prevent infection with HPV strains linked to cervical, anal, and throat cancers.

Most treatment vaccines are currently only available through clinical trials, according to Cancer.Net. The only cancer treatment vaccine approved by the FDA is one for advanced prostate cancer in men, according to the ACS.

Who receives immunotherapy?

Immunotherapy may be an option for you if:

  • A drug has been approved by the FDA for your type and stage of cancer.
  • You are enrolled in a clinical trial.

Immunotherapy is mostly used for patients whose cancers have recurred or spread to other parts of the body. These drugs are typically given after other mainstay treatments (like surgery and radiation) have been exhausted.

However, studies are looking at immunotherapy as a first-line therapy for some cancers. Dr. Caligiuri predicts these treatments may replace high-dose chemotherapy, radiation, and surgery, in some cases. “We’re not there yet, but that’s where it will be,” he says.

Immunotherapy side effects

Like all medicines, immunotherapy can cause side effects. The National Cancer Institute says the most common ones are skin reactions or flu-like symptoms. Other side effects include swelling, heart palpitations, sinus congestion, diarrhea, and increased infection risk. Severe or fatal reactions are rare.

Patients on immunotherapy ought to report any unusual changes in their health. If the immune system overreacts, it can damage healthy tissue and organs. Then drugs must be given to quiet the immune system. The key is “finding that right balance,” Dr. Caligiuri says.

Immunotherapy survival rate

For patients with certain blood cancers and solid tumors, immunotherapy may prolong life. By how much? Experts cannot readily cite an average or a range.

That’s because many factors are involved, Dr. Sabel explains. These include the type and stage of the cancer, the particular drug or drug combo used in treatment, and even the strength of the patient’s own immune system.

For patients with metastatic melanoma, a serious type of skin cancer that has spread to the brain or other organs, checkpoint inhibitors have shown impressive results. In a recent study, melanoma patients with brain metastases on checkpoint inhibitors had a four-year survival rate of 28.1%, versus 11.1% for those who did not receive immunotherapy.

CAR T-cell therapy is another bright spot. In 2018, ASCO named it the “Advance of the Year,” citing its lifesaving potential in leukemia, lymphoma, and lung cancer.

There’s still a lot to learn. Researchers want to know why some patients’ cancers stop responding to immunotherapy treatment, for example.

As for long-term survival with immunotherapy, “the jury is still out,” Dr. Caligiuri says.

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