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Sobi study did not meet primary endpoints

Guido Oelkers

Swedish Orphan Biovitrum (Sobi) has announced results from its phase 3 study of avatrombopag, an oral thrombopoietin (TPO) receptor agonist, in solid tumour cancer patients with chemotherapy-induced thrombocytopenia (CIT).

Though avatrombopag increased platelet counts relative to placebo as expected, the study did not meet the composite primary endpoint of avoiding platelet transfusions, chemotherapy dose reductions by 15 per cent or greater, and chemotherapy dose delays by four days or more. In the intent-to-treat population (full analysis set), 69.5 per cent and 72.5 per cent of avatrombopag and placebo subjects, respectively, were considered responders for the primary endpoint (p=0.72). In the per-protocol population, 85.0 per cent and 84.4 per cent of avatrombopag and placebo subjects, respectively, were considered responders for the primary endpoint (p=0.96).

Unexpected

It was unexpected that the placebo subjects would have such a low incidence of dose delays and dose reductions and additional data analyses are ongoing to understand this observation. Topline adverse event data for avatrombopag reinforce the existing safety profile and were comparable to that of placebo in this population of cancer patients receiving myelosuppressive chemotherapy.

“While we are disappointed that avatrombopag failed to show efficacy in CIT, we are deeply grateful to the patients, investigators, and clinical site staff who contributed to the study’s completion. Due to the lack of an approved treatment we firmly believe that avatrombopag could benefit patients with CIT. We were pleased to see that few patients required platelet transfusions or dose modifications in this study and were able to receive their chemotherapy without interruption,” says Guido Oelkers, CEO and President of Sobi. “We will continue to focus on the launches of the CLD and ITP indications and peak sales estimates remain unchanged given the potential of the product.”

About the phase 3 study

The phase 3 randomised, double-blind, placebo-controlled study was designed to evaluate the efficacy and safety of avatrombopag in subjects with chemotherapy-induced thrombocytopenia (CIT) receiving chemotherapy to treat ovarian, lung (small cell and non-small cell), and bladder cancer. The composite primary endpoint was the efficacy of avatrombopag in increasing platelet counts and therefore preventing the need for a platelet transfusion or chemotherapy dose reduction or delay in subjects with CIT. The secondary endpoint was safety. A total of 122 patients who developed Grade 3/4 thrombocytopenia following a previous cycle of chemotherapy were enrolled in 71 sites around the world.

Photo of Guido Oelkers: Sobi