Immunotherapy is given in several ways depending on the type of cancer and the specific treatment plan: through an IV drip, as a pill you swallow, as a cream applied to your skin, or in some cases directly into a body cavity like the bladder. The most common form for advanced cancers is intravenous infusion, which typically takes 30 to 90 minutes per session. Before treatment begins, your medical team will run tests on your tumor to determine which approach, if any, is likely to work for you.
How Immunotherapy Works in Your Body
Cancer cells survive partly by tricking your immune system into ignoring them. They do this by displaying certain proteins on their surface that send an “off” signal to your T cells, the immune cells responsible for hunting down threats. When a T cell encounters one of these proteins, it essentially stands down instead of attacking.
The most widely used immunotherapy drugs, called checkpoint inhibitors, block that “off” signal. Normally, a protein on the tumor cell (called PD-L1) binds to a matching protein on the T cell (called PD-1), telling the T cell to leave the tumor alone. Checkpoint inhibitors physically prevent that binding, so the T cell stays active and attacks the cancer. Another class of drugs targets a different checkpoint protein called CTLA-4, which works through a similar principle of releasing the brakes on your immune response.
Testing Before You Start
Not every cancer responds to immunotherapy, so your oncologist will order specific biomarker tests before recommending it. The most common is a PD-L1 test, which analyzes a sample of your tumor tissue to measure how much of the PD-L1 protein your cancer cells produce. If the percentage is too low, certain immunotherapy drugs are unlikely to help.
Results come in different scoring systems. A Combined Positive Score (CPS) measures PD-L1 on both tumor cells and nearby immune cells, while a Tumor Proportional Score (TPS) looks only at the percentage of tumor cells with high PD-L1 levels. Which scoring system matters depends on the drug being considered. For some immunotherapy drugs, PD-L1 testing is required before treatment can begin. For others, it’s recommended but not mandatory.
What an IV Infusion Session Looks Like
Most checkpoint inhibitor treatments are delivered intravenously at an infusion center or hospital outpatient clinic. A nurse places an IV line, and the drug drips into your bloodstream over 30 to 90 minutes, depending on the specific medication. Some sessions include pre-medications to reduce the chance of an infusion reaction.
Treatment schedules vary. Some drugs are given every two weeks, others every three or six weeks. You’ll sit in a chair or recliner during the infusion, and many people read, watch something on their phone, or nap. After the infusion, you’re typically monitored briefly and then go home the same day. Newer formulations are moving toward subcutaneous injections that take only a few minutes, which some patients may already have access to.
Other Ways Immunotherapy Is Delivered
Not all immunotherapy goes through an IV. Oral immunotherapy drugs come as pills or capsules you take at home on a set schedule. Topical immunotherapy is a cream applied directly to the skin, used primarily for very early-stage skin cancers. Intravesical immunotherapy is delivered directly into the bladder through a catheter, most commonly for early bladder cancer. Each route is matched to the type and location of the cancer being treated.
How CAR T-Cell Therapy Works
CAR T-cell therapy is a more intensive form of immunotherapy used for certain blood cancers. Instead of taking a drug that activates your existing immune cells, this approach removes your T cells, engineers them in a lab to recognize your specific cancer, and infuses them back into your body.
The process starts with a blood collection procedure called apheresis. A machine draws your blood, filters out the T cells, and returns the rest to your body. The collected cells are then sent to a specialized lab where they’re genetically modified to produce a receptor that locks onto cancer cells. This manufacturing step takes several weeks. During that time, you may receive a short course of chemotherapy to prepare your body to accept the modified cells. When the engineered T cells are ready, they’re infused back through an IV. Because the side effects can be significant, CAR T-cell therapy usually requires close monitoring in a hospital setting for at least a week or two after infusion.
Combining Immunotherapy With Chemotherapy
Immunotherapy is frequently paired with chemotherapy rather than used alone. There are two main approaches to combining them. In concurrent treatment, both the immunotherapy drug and the chemotherapy agents are given on the same day. In sequential treatment, one is given first and the other follows after an interval of more than 24 hours. Some oncologists prefer the concurrent approach because it mirrors the protocols used in large clinical trials, while others favor sequential dosing with the goal of improving effectiveness and reducing side effects. Which approach your oncologist recommends will depend on your specific cancer type and treatment plan.
How Long Treatment Lasts
The duration of immunotherapy varies widely. Many patients receive checkpoint inhibitors for one to two years if the cancer is responding and side effects are manageable. Stopping treatment is a careful decision. Patients who achieve a complete response (meaning no detectable cancer remains) and stay on treatment for at least a year tend to do well after stopping: roughly 84% remain progression-free for at least a year after elective discontinuation.
The picture is different for patients with only a partial response. Among those who stopped treatment with some cancer still detectable, about 56% saw their cancer progress within two years. Patients who had to stop early because of side effects also faced higher progression rates (around 45% within two years) compared to those who stopped electively (31%). These numbers underscore why oncologists are cautious about cutting treatment short, particularly when the cancer hasn’t fully disappeared.
Side Effects and When They Appear
Because immunotherapy works by activating your immune system, the most common side effects happen when that activated immune system attacks healthy tissue. These are called immune-related adverse events, and they can affect the skin, gut, liver, lungs, kidneys, and hormone-producing glands.
Side effects typically appear within the first 2 to 15 weeks of treatment, though the timing depends on what’s affected. Skin reactions and infusion-related reactions tend to show up first. Gut and neurological issues come next. Kidney problems and hormonal disruptions tend to appear later, usually 8 to 12 weeks in. Hormonal side effects are particularly notable because they take the longest to resolve and have the lowest resolution rate, meaning some patients need ongoing hormone replacement even after immunotherapy ends.
Combination regimens that use two checkpoint inhibitors together tend to cause side effects earlier than single-drug treatment. And while most side effects emerge within the first few months, they can occasionally appear months or even years after treatment ends. Severe side effects are relatively uncommon with single-agent therapy but occur more often with combination approaches. If side effects do develop, your oncologist may pause treatment, prescribe medications to calm the immune response, or in some cases discontinue immunotherapy altogether.