Pfizer is betting on a new breast cancer drug combo that, in a key mid-stage trial, cut the risk of the disease worsening or patients dying by about 40% for a particularly tough-to-treat group.
The investigational pill, atirmociclib, is an oral CDK4-selective inhibitor given alongside the hormonal therapy fulvestrant in people with metastatic breast cancer whose tumors had already stopped responding to existing CDK4/6 drugs. In the study, the atirmociclib and fulvestrant duo was pitted against either fulvestrant alone or the everolimus plus exemestane regimen, and the combo delivered a roughly 40% reduction in the risk of progression or death.
More than 90% of patients in the trial started atirmociclib within three months of stopping their prior CDK4/6 treatment, underscoring how quickly their disease had pushed past standard options. Pfizer described the safety profile as manageable, with 6.4% of patients discontinuing treatment because of side effects, according to KSL.
What Atirmociclib Does
Atirmociclib is designed to home in on CDK4, a protein that helps drive cancer cell division, while largely sparing CDK6. That selectivity is meant to reduce the blood-related side effects that can crop up with drugs that hit both CDK4 and CDK6. Preclinical work has suggested that focusing on CDK4 might allow higher dosing with fewer hits to patients' blood counts, according to Cell Research.
Pfizer says a large late-stage study of atirmociclib in newly diagnosed metastatic breast cancer is already underway and that the company plans to move the drug into earlier treatment settings if phase 3 testing confirms the benefit seen so far, according to Pfizer.
Trial Population And Safety
The mid-stage trial focused on patients whose cancer came back or worsened soon after treatment with other CDK4/6 inhibitors, a subgroup oncologists often describe as harder to treat and in urgent need of better options, as reported by KSL.
Earlier, smaller studies pairing atirmociclib with other hormone therapies have already shown encouraging signs of activity along with a tolerable safety profile, which helps explain why Pfizer moved relatively quickly into larger trials, according to OncLive.
Next Steps
Pfizer has cautioned that overall survival results from the mid-stage study are still early and not yet solid enough to draw firm conclusions, according to Pfizer. Independent experts say the drug will need to prove itself in phase 3 and hold up with longer follow-up before it can seriously challenge current standards of care.
Regulators and clinicians will be watching those larger trials closely. If the phase 3 data repeat the mid-stage benefit and the safety profile remains acceptable, atirmociclib could eventually move into earlier lines of treatment as part of a broader wave of next-generation endocrine strategies, according to Pharmaphorum.
.jpg){kind=link}