Mirum Pharmaceuticals, Inc. (MIRM) · Oct 13, 2026 · Other events
Above the bar — Primary endpoint met; all five prespecified secondary endpoints statistically significant
Mirum Pharmaceuticals’ EXPAND clinical trial met its primary endpoint and all five secondary endpoints, strengthening the case for a broader LIVMARLI label.
Mirum is using its established LIVMARLI franchise to expand beyond approved Alagille syndrome and PFIC indications into additional ultra-rare cholestatic liver diseases, while its broader pipeline advances other late-stage liver programs. This is a clean clinical win, not merely a primary-endpoint pass. EXPAND met its primary pruritus endpoint and achieved statistical significance across all five prespecified secondary endpoints, including the three tested in biliary atresia patients with a native liver. 〔0〕
| EXPAND result | Maralixibat | Placebo | Treatment effect | p-value |
|---|---|---|---|---|
| Change in ItchRO(Obs) severity score, all pediatric patients | -1.81 | -0.83 | -0.98 | 0.0004 |
| Relative change in total serum bile acids, overall population | -70.1% | -3.5% | -69.0% | <0.0001 |
| Change in ItchRO(Obs), biliary atresia/native liver subgroup | -2.16 | -1.01 | -1.15 | 0.0002 |
| Pruritus-improvement days, biliary atresia/native liver subgroup | 96.4% | 52.2% | 44.1% | 0.0045 |
The efficacy signal is broad and clinically relevant to the expansion thesis. The drug reduced itch severity by nearly one point versus placebo in the primary pediatric analysis and produced a 69.0% placebo-adjusted reduction in serum bile acids. The biliary-atresia/native-liver subgroup was at least as strong, which matters because that is a specific high-unmet-need population Mirum is trying to reach. 〔1〕
The main limitation is tolerability, not efficacy. Overall serious and grade 3-or-higher adverse-event rates were broadly similar between groups, but diarrhea was materially more common with maralixibat—64.0% versus 11.1% for placebo—and one treated patient discontinued. 〔2〕 〔3〕 This does not overturn the readout, but regulators and prescribers will still weigh the benefit against gastrointestinal burden in a small, 52-patient study.
The result advances a known catalyst into a regulatory opportunity. EXPAND enrollment and the expected fourth-quarter 2026 data timing were already public, so the timing was partly known; the new information is that the study cleared every stated efficacy measure rather than only confirming a narrow primary-endpoint success. Mirum has indicated that the next named step is a U.S. supplemental application in the first half of 2027.
Bottom line: EXPAND materially strengthens Mirum’s LIVMARLI expansion story: efficacy was consistent across itch, bile acids, and biliary atresia, with no new safety signal. The remaining work is regulatory execution and proving that the gastrointestinal side effects are manageable in broader use.
U.S. sNDA submission, first half of 2027
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