Immunotherapy: How it works and who it can help

Immunotherapy has changed the way some cancers are treated. Instead of attacking cancer cells directly in the way traditional chemotherapy often does, immunotherapy helps the body’s own immune system recognize, target, or attack cancer.

For some people, it can produce powerful and long-lasting responses. But immunotherapy does not work for every cancer or every patient, and whether it is appropriate depends on the type of cancer, its characteristics, biomarkers, previous treatments, and other individual factors.

What is immunotherapy?

Your immune system constantly looks for things that do not belong in your body, including infections and abnormal cells.

Cancer creates a difficult problem: cancer cells develop from your own cells. They can therefore be harder for the immune system to recognize as dangerous.

Cancer cells can also develop ways of escaping immune attack. For example, they may become less visible to immune cells or use biological signals that effectively tell immune cells to switch off.

Immunotherapy attempts to overcome some of these defenses and help the immune system act against the cancer.

How does immunotherapy work?

There isn’t just one type of immunotherapy.

One of the most important forms is immune checkpoint inhibition.

The immune system normally has biological “checkpoints” that prevent immune cells from becoming overactive and damaging healthy tissue.

Some cancers exploit these checkpoints.

For example, PD-1 is a checkpoint protein found on certain immune cells called T cells. PD-L1 can be present on cancer cells. When PD-L1 binds to PD-1, it can send an “off” signal that prevents the T cell from attacking.

Drugs called checkpoint inhibitors can block interactions such as PD-1/PD-L1, removing that signal and allowing T cells to attack cancer cells more effectively.

Immunotherapy isn’t one treatment

Several very different treatments fall under the immunotherapy umbrella.

They include checkpoint inhibitors, certain monoclonal antibodies, CAR T-cell therapy and other T-cell therapies, cancer treatment vaccines, and immune-system modulators.

CAR T-cell therapy, for example, involves collecting a patient’s T cells and modifying them in a laboratory so they can better recognize particular targets on cancer cells. The modified cells are then multiplied and returned to the patient.

This is very different from taking a checkpoint inhibitor, even though both approaches are called immunotherapy.

Which cancers can immunotherapy treat?

Immunotherapy is now used in the treatment of many cancers, but having cancer does not automatically mean immunotherapy will work or even be an appropriate option.

It can be used in certain situations involving cancers such as melanoma, lung cancer, kidney cancer, bladder cancer, colorectal cancer, some blood cancers and several others.

The exact indication matters enormously.

In modern cancer treatment, doctors increasingly look not only at where the cancer started, but also at the biological characteristics of the tumor.

Why biomarkers matter

Two people can have what appears to be the same type of cancer but respond very differently to immunotherapy.

One reason is biomarkers.

Depending on the cancer, doctors may test the tumor for particular molecular or genetic characteristics that can help predict whether certain treatments are likely to work.

The American Cancer Society notes that many immunotherapies target cancers with particular biomarkers.

That means the better question is often not simply:

“Does immunotherapy work for my cancer?”

but:

“Does my specific cancer have characteristics that make it likely to respond to a particular immunotherapy?”

Why doesn’t immunotherapy work for everyone?

This remains one of the biggest challenges in cancer immunotherapy.

Some tumors respond dramatically. Others respond only temporarily. Others do not respond at all.

Cancer can use multiple mechanisms to escape or suppress the immune system, and researchers are actively studying why resistance develops and how to predict which patients are most likely to benefit.

This is also why a story about one person’s extraordinary response to immunotherapy cannot predict what will happen to another person.

Can immunotherapy cure cancer?

Sometimes treatment is given with curative intent, and some patients can experience very durable responses.

But describing immunotherapy simply as a “cure for cancer” would be seriously misleading.

The goal of treatment depends on the cancer, its stage and the individual clinical situation. Immunotherapy may be used in an attempt to cure cancer, control it, reduce the chance of recurrence, shrink tumors, prolong survival, or relieve problems caused by cancer.

Is immunotherapy easier than chemotherapy?

Not necessarily.

The two treatments work differently and therefore tend to produce different patterns of side effects.

Because immunotherapy stimulates or alters immune activity, the immune system can sometimes attack healthy organs and tissues as well as cancer.

Potential immune-related effects can involve the skin, bowel, thyroid and other hormone-producing glands, liver, lungs and other organs. Some reactions can become serious and require prompt treatment.

So “immunotherapy doesn’t have chemotherapy side effects” should never be interpreted as “immunotherapy has no serious side effects.”

How do doctors know if it’s working?

Patients receiving immunotherapy are monitored using a combination of clinical assessment, blood tests, imaging such as CT or MRI scans, and other tests appropriate to the particular cancer.

Doctors look for changes in tumors as well as the patient’s overall condition and laboratory results.

The timing and type of monitoring depend on the cancer and treatment being used.

The bottom line

Immunotherapy is one of the most important advances in modern cancer treatment.

But immunotherapy is not a single drug, it is not appropriate for every cancer, and it does not work for everyone.

The important question is whether a particular immunotherapy has evidence for your specific type and stage of cancer and whether the tumor has biomarkers or other characteristics that make benefit more likely.

Treatment decisions should therefore be based on the exact diagnosis, pathology, molecular testing, previous treatments and discussion with the oncology team — not simply on the fact that immunotherapy has worked remarkably well for someone else.

Questions to ask your doctor