The short answer
Bispecific antibodies are lab-made proteins that grab a cancer cell with one arm and a T cell with the other, pulling the immune system in to attack. Because this can trigger cytokine release syndrome or neurologic side effects, the first doses are given in small step-up amounts, often with a hospital stay to monitor for reactions.
Bispecific antibodies are drugs with two 'arms' — one binds a cancer cell, the other binds a T cell, bringing them together so the immune system attacks the cancer.
Drugs in this class include epcoritamab, teclistamab, talquetamab, tarlatamab, and glofitamab, used for lymphoma, multiple myeloma, and some lung cancers.
The first doses are given as small 'step-up' amounts building toward the full dose, to lower the risk of a severe reaction.
Cytokine release syndrome (CRS) is a reaction from a sudden immune-system surge — it can cause fever, low blood pressure, and low oxygen, usually within the first cycle.
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The full explanation.
A new way to bring the immune system to the cancer
Bispecific antibodies are a fast-growing class of cancer drugs. Each one is a lab-made protein shaped like a "Y" with two different arms. One arm locks onto a protein found on cancer cells. The other locks onto a T cell, an immune cell that can kill abnormal cells once it is switched on. By holding both at the same time, the drug pulls the T cell right up against the cancer cell so it can attack.
This class includes epcoritamab, teclistamab, talquetamab, tarlatamab, and glofitamab. They treat cancers such as certain lymphomas, multiple myeloma, and some lung cancers, and more are being tested for other cancers. They are given as an injection or an infusion, usually on a repeating schedule. Treatment often continues for as long as it keeps working and side effects stay manageable.
Why the first doses are given in small steps
Bringing a large number of T cells into sudden, close contact with cancer cells can switch the immune system on very fast. If the very first dose were the full treatment dose, that surge could be dangerous. So treatment usually starts with one or more small "step-up" doses before the full dose. The smaller signal gives the immune system less to react to at once. That lowers the chance of a severe reaction, though it does not remove it.
Epcoritamab shows the pattern. For large B-cell lymphoma, its approved schedule starts with a tiny first dose, steps up a week later, and reaches the full dose a week after that. Every drug in this class has its own schedule, so ask your care team what yours will look like.
Cytokine release syndrome
Cytokine release syndrome, usually shortened to CRS, happens when newly activated immune cells release a flood of signaling proteins called cytokines. It can cause fever, chills, a racing heart, low blood pressure, or low oxygen levels. In the epcoritamab lymphoma studies, more than half of patients had CRS of some grade. Most CRS events happened during the first cycle, and the middle time to onset was about a day after a dose. CRS ranges from mild to severe. Care teams watch for it closely, because early treatment works well for most people — fluids, oxygen, or a medicine that blocks the cytokine signal.
Neurologic side effects (ICANS)
A smaller number of people develop neurologic side effects. These are grouped under the term ICANS, short for immune effector cell-associated neurotoxicity syndrome. It can look like confusion, unusual sleepiness, tremor, trouble writing a normal sentence, or trouble finding words. These symptoms usually appear within the first few days after a dose. Like CRS, ICANS is treatable, most often with steroids. It does need prompt review, so tell your care team at once about any sudden change in thinking, memory, or coordination.
Why hospital monitoring is common early on
CRS and ICANS cluster around the first full-strength doses. Many treatment centers therefore plan a short hospital stay around those doses, even when later doses are given in the outpatient clinic. During that stay the team checks vital signs often and can start treatment the moment a reaction begins. This is a standard safety step built into how these drugs are used. It is not a sign that something has gone wrong.
When to get help sooner
Keep the 24-hour number on you for the days after every dose, and especially through step-up dosing and the first cycle.
- Call 911 or go to an emergency department if you cannot be woken properly, or have a seizure, or your breathing is fast and hard, or you feel faint with a racing heart. Those can mean severe cytokine release syndrome.
- Get seen straight away — the 24-hour number, or an emergency department if you cannot reach anyone — if your temperature reaches 100.4°F (38°C) or higher, or chills set in, in the days after a dose. Fever is usually the first sign of CRS, and onset is typically about a day after dosing. It can also be the only sign of infection, which the CDC treats as an emergency during cancer treatment. Do not wait to see whether it settles.
- Call your care team the same day if anyone around you notices confusion, unusual drowsiness, tremor, or difficulty writing a normal sentence or finding words. Those are the neurologic changes grouped as ICANS, and they need prompt review.
- Call your care team within a day or two if headache, aching, poor appetite or a low-grade temperature lingers, even once you are past the early doses.
Sources
Words to know
Tap any term to see what it means.
Common questions
What does 'bispecific' mean?
It means the antibody has two different binding sites. One site attaches to a protein on the cancer cell; the other attaches to a T cell, a type of immune cell. By holding both at once, the drug brings the T cell close enough to attack the cancer cell.
Why do I need a hospital stay for the first doses?
The first full-strength doses carry the highest risk of cytokine release syndrome and neurologic side effects, which can develop within a day of dosing and need fast treatment. Many centers admit patients for 24 to 48 hours around these early doses so vital signs and symptoms can be watched closely and treated right away if they appear.
What is cytokine release syndrome?
It is a reaction that happens when the immune system activates suddenly and releases a large amount of signaling proteins called cytokines. It can cause fever, chills, a fast heartbeat, low blood pressure, or trouble breathing. Most cases are manageable with monitoring and medicine, and it is most common after the first one or two doses.
What is ICANS?
ICANS stands for immune effector cell-associated neurotoxicity syndrome. It is a set of neurologic side effects — such as confusion, tremor, difficulty writing or speaking, or drowsiness — that can occur with bispecific antibodies and related immune therapies. It is usually treatable but needs prompt evaluation.
Do all bispecific antibodies work the same way?
The general idea is shared, but each drug targets a different pair of proteins and is approved for different cancers. Dosing schedules, monitoring requirements, and typical timing of side effects vary by drug, so ask your care team about the specific medicine you are being offered.
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Last updated: 2026-08-19Next planned review: 2027-02-03
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and checked line by line against the sources listed on it. That confirms the sources support what the page says. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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