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In the phase III HBI-8000-303 trial, adding the investigational HDAC inhibitor HBI-8000 to nivolumab extended median progression-free survival by 4.3 months compared with nivolumab and placebo. Severe treatment-related adverse events were more common with the combination, and overall-survival data are not yet mature.
A phase III trial found that adding the investigational HDAC inhibitor HBI-8000 to nivolumab lengthened progression-free survival for people with unresectable stage III or IV melanoma, meeting the study’s primary endpoint. After a median follow-up of 37 months, median progression-free survival was 11.66 months with the combination and 7.36 months with nivolumab plus placebo, while severe treatment-related side effects were substantially more frequent with HBI-8000.
The randomized HBI-8000-303 trial enrolled 404 patients at 123 sites across 15 countries. Participants had not previously received a PD-1, PD-L1 or other immune checkpoint inhibitor. They were assigned to nivolumab with either HBI-8000 or placebo and followed until their cancer progressed or treatment toxicity became unacceptable. Progression-free survival was the primary endpoint.
The 4.3-month difference in median progression-free survival corresponded to a 27% reduction in the hazard of progression or death in the HBI-8000 group, according to the reported analysis (95% confidence interval 0.56–0.95; P=0.0141). At two years, 41.3% of patients receiving HBI-8000 plus nivolumab were alive without disease progression, compared with 28.7% in the control group.
Among patients whose lactate dehydrogenase (LDH) levels were normal at the start of the trial, median progression-free survival was 20.04 months with the combination. Two-year progression-free survival in this subgroup was 47.2%, versus 32.6% with nivolumab and placebo. The trial report said about two-thirds of participants had normal baseline LDH; subgroup findings do not establish that every patient with normal LDH will receive the same benefit.
Objective response rates were 41.4% with HBI-8000 and 32.3% with placebo, with the difference attributed to more complete responses in the combination group: 14.3% versus 7.0%. The trade-off was toxicity. Grade 3 or 4 treatment-related adverse events occurred in 54.8% of patients receiving HBI-8000 and 17.9% of controls. Adverse events led to treatment discontinuation in 14.1% and 5.0%, respectively. Severe thrombocytopenia and neutropenia were also more frequent with HBI-8000.
A Longer Interval Before Progression
For patients with unresectable melanoma, delaying cancer progression can mean more time before a treatment change is needed. The trial’s median PFS difference of 4.3 months and two-year results suggest the combination may offer a meaningful disease-control benefit over nivolumab alone for some patients. The reported advantage was also seen across nearly all analyzed patient subgroups, although subgroup results warrant careful interpretation.
The findings do not yet show whether HBI-8000 helps patients live longer. Overall-survival results are immature, and the added benefit must be weighed against a marked increase in severe adverse events and treatment discontinuations. The data therefore inform treatment decisions but do not, on their own, settle the combination’s place in routine care.
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From Early Study to Phase III
The phase III study followed an earlier phase Ib/II trial of HBI-8000 with immunotherapy in patients with advanced melanoma who had not received anti-PD-(L)1 treatment. That smaller study reported an objective response rate of 65.8% and no unexpected toxicity; the larger randomized trial provides a comparison with nivolumab plus placebo.
HBI-8000 is an investigational histone deacetylase (HDAC) inhibitor. At the European Society for Medical Oncology congress in Madrid, invited discussant Olivier Michielin of Geneva University Hospital described a biological rationale for combining HDAC inhibition with PD-1 blockade: HDAC inhibitors may affect antigen presentation and the tumor environment in ways that could make cancer cells more susceptible to immune attack. That rationale is not itself proof of clinical benefit.
The report compared the two-year progression-free survival results with earlier melanoma trials, including CheckMate 067 and RELATIVITY-047. Those comparisons provide context, but they are not direct head-to-head evidence. The current study’s overall-survival data have not matured, limiting comparisons of survival outcomes.
““While GI [gastrointestinal] toxicities are certainly more common with this combination, these adverse events tend to be manageable with low rates of grade 3 and 4 nonhematologic adverse events.””
— Nikhil Khushalani, MD, Moffitt Cancer Center
Survival and Safety Still Developing
The report does not provide mature overall-survival results, so it remains unknown whether the longer progression-free survival translates into patients living longer. Further follow-up is also needed to clarify how the benefit and harms balance over time.
Although Khushalani described many gastrointestinal adverse events as manageable, the trial recorded higher rates of severe treatment-related events and discontinuation with HBI-8000. Reported grade 3 or 4 hematologic events included neutropenia in 16.6% of the combination group versus 0.5% of controls, and thrombocytopenia in 7.5% versus none. The congress report does not establish which individual patients are most likely to experience serious toxicity, or how clinicians should select and adjust treatment for them.
More Follow-Up Before Treatment Decisions
Researchers are expected to continue tracking the trial population, with overall survival and longer-term toxicity among the key information needed to assess the treatment’s full effect. Michielin said the evolving dataset should be considered carefully in the coming months. The available report does not specify a date for a further analysis or regulatory decision.
For now, the findings are phase III trial results presented at a medical congress. Any decision about using the combination should account for a patient’s circumstances and the observed side-effect rates; the report alone does not establish a new regulatory approval or a universal treatment recommendation.
Key Questions
What did the HBI-8000 melanoma trial find?
The phase III trial found that HBI-8000 plus nivolumab improved progression-free survival compared with nivolumab plus placebo. Median progression-free survival was 11.66 months versus 7.36 months.
How many patients took part?
The randomized study enrolled 404 people with unresectable stage III or IV melanoma at 123 sites in 15 countries. Participants had not previously received an immune checkpoint inhibitor.
Did the combination cause more side effects?
Yes. Grade 3 or 4 treatment-related adverse events were reported in 54.8% of the HBI-8000 group and 17.9% of the placebo group. Treatment discontinuations due to treatment-related adverse events were also more common with HBI-8000.
Does the trial show that HBI-8000 helps patients live longer?
That is not yet known. The reported overall-survival data are immature; the main result so far is an improvement in progression-free survival.
Is HBI-8000 approved for melanoma?
The source describes HBI-8000 as investigational and reports phase III trial findings. It does not report a regulatory approval for the drug.
Source: rss
