Disc Medicine's bitopertin hits all endpoints in pivotal Phase 3 APOLLO trial in EPP
What's the deal? On 19 October 2026, Disc Medicine reported positive topline results from APOLLO, its pivotal Phase 3 trial of bitopertin in erythropoietic protoporphyria (EPP) and X-linked protoporphyria (XLP). These are rare inherited conditions in which a build-up of light-sensitive molecules called porphyrins in the blood makes skin react painfully to sunlight. The trial hit all its primary and secondary endpoints: bitopertin reduced whole-blood levels of the photosensitiser protoporphyrin IX by 41.4% versus placebo (p<0.0001) and increased average monthly pain-free time in light by 12.2 hours (p=0.0010) at month 6, alongside statistically significant falls in phototoxic reactions and improvements in quality-of-life measures.
Why it matters: Bitopertin works by blocking an enzyme involved in porphyrin production, tackling the root cause of the disease rather than just the symptoms. It was generally well tolerated, with dizziness the most common side effect and no serious treatment-related events above grade 3. Disc Medicine now plans to resubmit a New Drug Application to the US FDA by the end of 2026, with a decision anticipated by mid-2027 — a re-do after the agency previously rebuffed the drug. There is currently no cure for EPP and only one approved therapy, making a second treatment option clinically significant for the roughly one in 75,000 people affected.
