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In a 404-patient phase III trial, adding investigational HDAC inhibitor HBI-8000 to nivolumab extended median progression-free survival to 11.66 months, from 7.36 months. 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 improved progression-free survival for people with unresectable melanoma, increasing median time without disease progression from 7.36 to 11.66 months. The result met the study’s primary endpoint, but the combination also brought substantially more severe treatment-related side effects, and its effect on overall survival is not yet known.
The international HBI-8000-303 trial randomized 404 people with unresectable stage III or IV melanoma to receive nivolumab with either HBI-8000 or placebo. Participants had not previously received a PD-1/PD-L1 inhibitor or another immune checkpoint inhibitor. The study took place at 123 sites in 15 countries, with a median follow-up of 37 months. Progression-free survival, or PFS, was the primary endpoint.
Median PFS was 11.66 months in the HBI-8000 group and 7.36 months in the control group, a 4.3-month difference. The analysis reported a 27% reduction in the hazard of progression or death (95% confidence interval 0.56-0.95; P=0.0141). At 24 months, 41.3% of patients receiving HBI-8000 and 28.7% receiving placebo remained alive without progression.
About two-thirds of participants had normal lactate dehydrogenase (LDH) levels at baseline. In that subgroup, median PFS with the combination was 20.04 months; the 24-month PFS rates were 47.2% with HBI-8000 and 32.6% with placebo. The report said the PFS benefit in patients with normal LDH represented a 35% reduction in the hazard (95% CI 0.47-0.90; P=0.0082). Subgroup findings do not establish that every patient will receive the same benefit.
Objective response rates were 41.4% with HBI-8000 and 32.3% with placebo. The difference was associated with more complete responses in the combination arm, 14.3% versus 7.0%. These response results were secondary to the primary PFS finding and do not by themselves show that treatment extends life.
Balancing Longer Disease Control and Toxicity
The results suggest that an oral HDAC inhibitor could add disease control to nivolumab, a PD-1 immunotherapy, for people with melanoma that cannot be removed surgically. The reported PFS difference and the 24-month rates offer a measure of how long patients remained alive without documented progression, an outcome that can inform treatment discussions while survival data are still pending.
The benefit must be weighed against a clear increase in harm. Grade 3 or 4 treatment-related adverse events occurred in 54.8% of patients on HBI-8000, compared with 17.9% in the control group. Treatment-related events led to discontinuation in 14.1% versus 5.0%. Severe blood-related effects included neutropenia (16.6% versus 0.5%) and thrombocytopenia (7.5% versus 0%). These rates make toxicity, monitoring and the possibility of dose changes central to assessing the regimen.
The findings could influence consideration of first-line options for advanced, unresectable melanoma, but they do not settle the choice of treatment. The study report describes encouraging PFS results; the immature overall-survival evidence and side-effect burden remain important limits on what can be concluded.
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How HBI-8000 Fits Melanoma Treatment
HBI-8000 is an investigational histone deacetylase (HDAC) inhibitor. The rationale for combining this drug class with PD-1 blockade is that HDAC inhibitors may affect cancer-cell antigen presentation and how susceptible tumor cells are to immune attack, while also changing the tumor microenvironment. Those mechanisms provide a scientific rationale, not proof of how much each effect contributed to the trial outcome.
The phase III study followed a smaller phase Ib/II trial in anti-PD(L)1-naive advanced melanoma. That earlier study reported an objective response rate of 65.8% and no unexpected toxicity; the larger randomized trial provides a comparison with nivolumab plus placebo. The invited discussant, Olivier Michielin of Geneva University Hospital, said the two-year results compared favorably with results from CheckMate 067 and RELATIVITY-047, studies that established benchmarks in unresectable melanoma. Such cross-trial comparisons are not the same as a direct randomized comparison between treatments.
Patients in HBI-8000-303 had a median age of 67, and men made up 60% to 65% of the study population. Roughly half had PD-L1-positive tumors, and about 60% had clinical M0/M1a/M1b disease. The trial’s population and eligibility rules help define who the results directly describe; they do not establish outcomes for people previously treated with checkpoint inhibitors.
“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, of Moffitt Cancer Center, reporting the findings at the ESMO congress
Survival and Long-Term Safety Still Pending
Overall-survival data remain immature, so the study has not established whether adding HBI-8000 helps patients live longer. The report gives no mature overall-survival comparison or final survival estimate. Longer follow-up is also needed to clarify how durable the PFS difference is and whether later data change the balance between benefit and harm.
The available report does not provide every detail needed to judge the treatment’s place in practice, including a full account of longer-term adverse events or how the results will translate into regulatory and guideline decisions. Although the presenter described many gastrointestinal effects as manageable, the high rate of severe treatment-related events and the greater rate of treatment discontinuation remain documented concerns. The trial results do not guarantee an individual patient’s response.
Follow-Up Will Test the Full Benefit
Researchers are expected to continue following participants for overall survival and longer-term toxicity. Those data will help determine whether the observed extension in progression-free survival is accompanied by a survival benefit, and provide a fuller account of treatment discontinuation and adverse effects over time.
For now, the phase III result supports the reported PFS advantage in the trial population, while treatment decisions require weighing that outcome against the combination’s higher toxicity. Clinicians and patients will need to consider the full evidence as it develops; the source report does not state a specific regulatory decision or date for one.
Key Questions
What did the HBI-8000 melanoma trial find?
The phase III trial found median progression-free survival of 11.66 months with HBI-8000 plus nivolumab, compared with 7.36 months with nivolumab plus placebo. The PFS result met the study’s primary endpoint.
Does the trial show that HBI-8000 helps patients live longer?
That has not been established. The trial’s overall-survival data are immature, so it is not yet clear whether the PFS improvement translates into longer life.
What side effects were reported?
Grade 3 or 4 treatment-related adverse events occurred in 54.8% of the HBI-8000 group and 17.9% of the placebo group. Severe neutropenia and thrombocytopenia were more frequent with HBI-8000, and treatment-related events led more patients to stop treatment.
Who was studied?
The trial enrolled 404 people with unresectable stage III or IV melanoma who had not previously received a PD-1/PD-L1 inhibitor or another immune checkpoint inhibitor. Results may not apply directly to people outside those criteria.
Is HBI-8000 an established treatment?
HBI-8000 is described in the report as investigational. The trial result does not, by itself, establish a regulatory approval or confirm that the combination is a standard option; the source report does not specify a regulatory decision.
Source: medpagetoday.com
