In mantle cell lymphoma (MCL), ibrutinib plus venetoclax significantly improved the complete response rate, compared with what has been previously reported for ibrutinib alone, according to results of a phase 2 study.

Clinical outcomes with the combination seem superior to previously reported results for either treatment alone, said lead investigator Constantine S. Tam, MBBS, MD , of the Peter MacCallum Cancer Centre, Melbourne, and his coinvestigators.

“The results of our study, which used a historical cohort as a control, are consistent with the notion that the combination of ibrutinib and venetoclax is highly effective in mantle-cell lymphoma,” the investigators wrote in the New England Journal of Medicine .

The BTK inhibitor ibrutinib and the BCL2 inhibitor venetoclax are two of the most active agents for this B-cell cancer, investigators reported. The rationale for combining the agents is “compelling” because they affect different critical pathways in the malignant B cell.

Both agents have demonstrated complete response rates of 21% in previous studies of relapsed or refractory MCL, and preclinical studies suggest the combination of ibrutinib and venetoclax would be synergistic.

In the present single-group, phase 2 study, 24 patients with MCL (23 relapsed or refractory, 1 previously untreated) started ibrutinib 560 mg daily; at 4 weeks, venetoclax was started at a low dose and increased to 400 mg daily.

The study primary end point – complete response rate at week 16 assessed by CT – was 42%, compared with 9% for ibrutinib monotherapy in the phase 2 PCYC-1104-CA study (P less than .001).

Computed tomography assessment was used for the primary end point to allow comparison to the ibrutinib monotherapy study, which did not use positron emission tomography for restaging. “Our study was designed to have 80% power to reject a complete response rate of 9% (at a one-sided alpha level of 0.05) if the rate of complete response was at least 30%,” the investigators noted.

Complete response rate assessed by positron emission tomography at week 16 was 62%, and was 71% overall.

In all, 67% of patients had absence of minimal residual disease by flow cytometry. At 15 months, 78% of the responses were ongoing, and at 18 months, 57% of patients were alive and progression free.

“Such outcomes appear to be substantially better than those that have been reported for ibrutinib or venetoclax monotherapy,” the investigators wrote.

The combination had side effects that are “acceptable to both patients and physicians,” investigators wrote. Side effects, usually low grade, included diarrhea in 83% of patients, fatigue in 75%, and nausea or vomiting in 71%. Tumor lysis syndrome was seen in two patients.

Whether ibrutinib plus venetoclax is superior to ibrutinib alone is being formally evaluated in an ongoing phase 3 study .

Janssen and AbbVie partially funded the current phase 2 study. Dr. Tam reported financial ties to Janssen, AbbVie, and Pharmacyclics. Other study authors reported financial ties to various pharmaceutical companies.

SOURCE: Tam C et al. N Engl J Med. 2018;378:1211-23.


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