Diarrhea and Cilta-Cel (Carvykti): What Patients Need to Know

The CAR T-cell therapy ciltacabtagene autoleucel (Carvykti), also known as cilta-cel, can be a life-saving treatment for many people with relapsed or refractory multiple myeloma. Like many cancer treatments, cilta-cel can have severe side effects. Cilta-cel can cause diarrhea and other gastrointestinal (GI) symptoms. For some people, this side effect can be life-threatening.

Research suggests up to 10 out of every 100 people who receive cilta-cel will develop severe GI symptoms. In this article, you will learn why cilta-cel causes diarrhea and GI symptoms, what to watch for and when to call your doctor, and what the latest research says. 

How cilta-cel causes diarrhea

When cilta-cel causes diarrhea, it is usually part of a cluster of GI symptoms. Together, these symptoms are called immune effector cell-associated enterocolitis or IEC-EC. 

“IEC-EC is an emerging complication arising after cilta-cel CAR T-cell therapy, which can be life threatening. We are still working to understand why this happens in these patients,” said Dr. Mark Leick, a hematologist at Massachusetts General Hospital. 

IEC-EC is most commonly caused by cilta-cel. But cases have been reported with other CAR-T therapies. During CAR T-cell therapy, a patient’s T cells are removed from the body. They are then modified in a lab to better fight myeloma cells. The T cells are infused back in the body. Sometimes, these modified T cells can attack healthy cells. This includes cells in the GI tract.  

In October 2025, the U.S. Food and Drug Administration (FDA) added a Boxed Warning to the cilta-cel label. This warning alerts doctors and patients about the risk of IEC-EC. Boxed Warnings are also called Black Box Warnings. They notify doctors and patients about serious and life-threatening side effects of treatments. 

In a message about the new warning, the FDA added, "FDA has determined that the overall benefit of CARVYKTI continues to outweigh the potential risks for the approved use, including overall survival benefit in patients treated with CARVYKTI." 

Dr. Leick emphasized this as well. “I do want to stress that while this side effect can be serious in some patients, cilta-cel, on net, is an extremely effective therapy for multiple myeloma in which the vast majority of patients have incredible anti-tumor responses,” said Dr. Leick. 

What are the signs and symptoms of IEC-EC?

If you have had cilta-cel therapy or another CAR-T treatment, you may wonder what IEC-EC is like. This is especially true because occasional GI problems, such as stomach aches and diarrhea, are normal for everyone. 

In one of the largest studies of patients with the condition, researchers looked at 14 people with IEC-EC. In the study, 13 patients had received cilta-cel, and 1 had received ide-cel. Ide-cel is another CAR-T therapy.

IEC-EC started between 1 and 3 months after CAR-T therapy. The symptoms were: 

• Sudden diarrhea that did not improve. 
• Only one patient had blood in their stool.
• 10 out of 14 patients reported abdominal pain.
• All patients who had biopsies (13 total) showed inflammation in at least one part of the GI tract.

If you have had cilta-cel or another type of CAR-T therapy, you should tell your doctor right away if you have: 

• Diarrhea
• Abdominal pain
• Nausea
• Cramping
• Blood or mucus in the stool
• Other changes in bowel habits
• Fever
• Swollen abdomen
• Constipation

“Many patients receive cilta-cel CAR T-cell therapy at large regional medical institutions, and then after several weeks, return to their local oncologist who may not be as familiar with the longer-term and rare complications after this drug,” said Dr. Leick, emphasizing how important it is to track symptoms and tell your care team if any develop.

 “There are many causes for diarrhea among myeloma patients who recently got cilta-cel that are not IEC-EC,” he noted. “It is important that these other causes be excluded before attempting any IEC-EC-directed therapies.” 

How is diarrhea after cilta-cel treated?

Doctors are still learning the best way to treat diarrhea and IEC-EC after CAR-T therapy. Finding effective treatments for IEC-EC is important, because it can be very dangerous. Research suggests 36% to 50% of people who develop diarrhea that cannot be controlled after CAR-T will die from the condition.

Many doctors treat IEC-EC the same way as other types of colitis caused by immunotherapy. 

For example, immunotherapies called checkpoint inhibitors also cause a type of colitis. These treatment guidelines recommend: 

• Over-the-counter medications for diarrhea, such as loperamide
• Corticosteroids
• Infliximab, an immunosuppressant
• Vedolizumab, a biologic used to treat colitis 

Patients should also have an endoscopy to determine the best possible treatment. If you develop severe diarrhea, you may need treatment in the hospital. This is to help manage dehydration and other complications.

Latest research points to ruxolitinib as a possible treatment option for severe diarrhea after CAR-T

In a recent study published in Blood, Dr. Leick and other researchers studied 5 patients who developed severe diarrhea after receiving cilta-cel. 

Three out of the 5 patients were treated with ruxolitinib (Jakafi). Ruxolitinib is a JAK inhibitor that is approved to treat graft-versus-host disease (GVHD). All three of the patients treated with ruxolitinib improved quickly. For 2 out of 3 patients who had pre- and post-treatment biopsies, they also had fewer CAR-T cells in the GI tract after ruxolitinib. 

While this is a small study, it shows that there may be treatment options for this group of high-risk patients. 

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Sources: 

Immune effector cell-associated enterocolitis (IEC-EC) across CAR-T products in myeloma and lymphoma: A real world pharmacovigilance analysis

FDA Approves Labeling Changes that Include a Boxed Warning for Immune Effector Cell-associated Enterocolitis Following Treatment with Ciltacabtagene Autoleucel (CARVYTKI, Janssen Biotech, Inc.)

Immune effector cell-associated enterocolitis following chimeric antigen receptor T-cell therapy in multiple myeloma

Management of Immune-Related Adverse Events in Patients Treated With Immune Checkpoint Inhibitor Therapy: ASCO Guideline Update

Ruxolitinib for ciltacabtagene autoleuce-associated refractory diarrhea