AMSTERDAM – A combination of rituximab and the BRAF inhibitor vemurafenib could be the one-two punch needed for relapsed or refractory hairy cell leukemia (HCL), according to investigators.
Among evaluable patients treated with this combination, 96% achieved complete remission, reported lead author,, of the University and Hospital of Perugia, Italy.
This level of efficacy is “clearly superior to historical results with either agent alone,” Dr. Tiacci said during a presentation at the annual congress of the European Hematology Association, citing previous complete response rates with vemurafenib alone of 35%-40%. “[This combination] has potential for challenging chemotherapy in the frontline setting,” he said.
The phase 2 trial involved 31 patients with relapsed or refractory HCL who had received a median of three previous therapies. Eight of the patients (26%) had primary refractory disease. Patients received vemurafenib 960 mg, twice daily for 8 weeks and rituximab 375 mg/m2, every 2 weeks. After finishing vemurafenib, patients received rituximab four more times, keeping the interval of 2 weeks. Complete remission was defined as a normal blood count, no leukemic cells in bone marrow biopsies and blood smears, and no palpable splenomegaly.
Out of 31 patients, 27 were evaluable at data cutoff. Of these, 26 (96%) achieved complete remission. The investigators noted that two complete responders had incomplete platelet recovery at the end of treatment that resolved soon after, and two patients had persistent splenomegaly, but were considered to be in complete remission at 22.5 and 25 months after finishing therapy.
All of the complete responders had previously received purine analogs, while a few had been refractory to a prior BRAF inhibitor (n = 7) and/or rituximab (n = 5).
The investigators also pointed out that 15 out of 24 evaluable patients (63%) achieved complete remission just 4 weeks after starting the trial regimen. Almost two-thirds of patients (65%) were negative for minimal residual disease (MRD). The rate of progression-free survival at a median follow-up of 29.5 months was 83%. Disease progression occurred exclusively in patients who were MRD positive.
The combination was well tolerated; most adverse events were of grade 1 or 2, overlapping with the safety profile of each agent alone.
Reflecting on the study findings, Dr. Tiacci suggested that the combination could be most effective if delivered immediately, instead of after BRAF failure.
“Interestingly,” he said, “the relapse-free survival in patients naive to a BRAF inhibitor remained significantly longer than the relapse-free interval that patients previously exposed to a BRAF inhibitor enjoyed, both following monotherapy with a BRAF inhibitor and following subsequent combination with rituximab, potentially suggesting that vemurafenib should be used directly in combination with rituximab rather than being delivered first as a monotherapy and then added to rituximab at relapse.”
Randomized testing of the combination against the chemotherapy-based standard of care in the frontline setting is warranted, the investigators concluded.
Dr. Tiacci reported financial relationships with Roche, AbbVie, and Shire.
SOURCE: Tiacci E et al. EHA Congress, Abstract S104.