Of 45 patients, 57% reached U-MRD at 12 months, and 55% reached complete remission, according to the study, published in Leukemia.
By adding venetoclax, “you can get very deep remissions in high-risk patients with ibrutinib,” lead author Philip A. Thompson, MBBS, a hematologist-oncologist with the University of Melbourne and Peter MacCallum Cancer Center, also in Melbourne, said in an interview. “This is a significant advance for really high-risk patients.”
According to Dr. Thompson, Bruton’s tyrosine kinase inhibitors like ibrutinib have revolutionized the treatment of high-risk CLL by forcing the disease into remission for several years and allowing patients to avoid stem cell transplants. “But the drug doesn’t eradicate the disease,” he said, “so eventually these patients develop progression.”
The current hope, he said, is to use a combination therapy like ibrutinib and venetoclax to send CLL into remission with lower chance of drug resistance and then allow patients to stop taking the medications.
Previous research has supported the combination of ibrutinib and venetoclax in CLL in the frontline setting, and the European Commission approved it in 2022 for that use. But “ours is the first [study] that looked at patients who’ve been on ibrutinib for a long time and added venetoclax,” Dr. Thompson said. In some cases, he said, patients in the study had been on ibrutinib for several years.
For the new study, researchers at the University of Texas MD Anderson Cancer Center in Houston – where Dr. Thompson used to work – tracked 45 patients (average age, 68.5 years; 51-80 years) with CLL or small lymphocytic lymphoma who had MRD but no clinical disease progression. They all had at least 1 high-risk feature such as a mutated TP53. They’d been on ibrutinib for a median of 32 months (12-73 months), and two were in complete remission but with MRD.
An intention-to-treat analysis found that 71% reached U-MRD when they finished taking venetoclax. “We were actually pleasantly surprised by the high rate of undetectable MRD,” Dr. Thompson said.
At a median 41-month follow-up, 11% of patients had progressed, but none had died of CLL or Richter transformation, a deadly complication of CLL. “The main side effects were neutropenia and diarrhea, which we were manageable,” Dr. Thompson said.
It’s not clear why the drug combination is especially effective, he said, but it may be because the medications are synergistic. According to the National Cancer Institute, synergy in medicine refers to “the interaction of two or more drugs when their combined effect is greater than the sum of the effects seen when each drug is given alone.”
The findings suggest that “you can get deep remissions in high-risk patients with ibrutinib and venetoclax with very with good tolerability and very low risk of on-treatment progression,” Dr. Thompson said. “We don’t yet have enough progression events to talk about retreatment data, but we do feel that retreatment with Bruton’s tyrosine kinase inhibitors – plus or minus venetoclax – will be successful in the vast majority of patients.”
The combination can be given off label in the United States, Dr. Thompson added. As for expense, adding venetoclax will double the cost of ibrutinib. The two drugs are some of the most expensive medications in the world. But patients will save money if they can stop therapy when they reach remission.
In an interview, hematologist-oncologist Kerry A. Rogers, MD, of Ohio State University, Columbus, who is not involved with the study, praised the research: “While small, this study does say quite a bit about this as a strategy to help people discontinue ibrutinib prior to resistance developing.”
She noted that Bruton’s tyrosine kinase inhibitors “are generally given as a continuous monotherapy, and venetoclax is usually given for a fixed duration in combination with an anti-CD20 antibody.”
Going forward, she said, “the fact that the study was in high-risk patients who have the most to gain from such a combination suggests that similar or better rates of undetectable minimal residual disease might be seen in non–high-risk groups. Additional follow-up should be reported as well as use of this strategy in a larger group of patients before this should be considered a standard approach.”
AbbVie funding the study and provided study drugs. MD Anderson Cancer Center conducted the study and discloses funding from the National Cancer Institute. Dr. Thompson reported ties with AbbVie, Pharmacyclics, Lilly, Adaptive Biotechnologies, Janssen, BeiGene, and Genentech. The other study authors reported multiple disclosures. Dr. Rogers disclosed relationships with Genentech, AbbVie, Novartis, Janssen, Pharmacyclics, BeiGene, Lilly, and AstraZeneca.