One in every 3,800 people is born with a disorder that makes their blood vessels malformed and fragile. The disease is called hereditary hemorrhagic telangiectasia, and in 2026 it still has zero approved treatments anywhere in the world. On August 11, a 13-person Swiss startup called Vaderis Therapeutics closed a $152 million Series B and opened a global Phase 3 trial that could change that number.
The cash funds engasertib, an oral AKT1/2 inhibitor, through a global randomized Phase 3 trial (HEROIC) and a potential U.S. approval in hereditary hemorrhagic telangiectasia (HHT), a rare vascular disorder with no approved therapy.
A 75-patient proof-of-concept study published in the New England Journal of Medicine cut epistaxis frequency by about 27% at the higher dose, versus 18% on placebo. The open question is whether Phase 3 reproduces that effect at scale.
The disease with no therapy to name
HHT is a genetic disorder of the vasculature. Patients carry congenital anomalies where blood vessels form poorly and rupture easily. The most visible symptom is epistaxis, nosebleeds that can be frequent and severe, alongside anemia and arteriovenous malformations in the lungs, liver and gastrointestinal tract.
Until a few weeks ago, the standard answer for patients was management, not treatment. No drug has ever been approved specifically for HHT.
Vaderis was founded in 2019 to build that first therapy. The company raised just over $22 million in 2020, read out Phase 1 data in 2024, and now holds the most advanced molecule in the field. Its drug, engasertib, is an oral selective allosteric inhibitor of AKT1/2, a signaling enzyme that sits upstream of the abnormal vessel growth the disease depends on.
What the proof-of-concept actually showed
The scientific backbone of the $152 million round is a study published in the New England Journal of Medicine in late 2025. It randomized 75 patients with moderate-to-severe HHT to 30 mg of engasertib, 40 mg, or placebo, taken once daily for 12 weeks.
12-week reduction in nosebleed frequency
Mean change from baseline with the higher dose, versus placebo, in the NEJM proof-of-concept study. Duration fell 41.4% vs 23.8% on placebo. · New England Journal of Medicine, 2025
The result was positive but not overwhelming. Epistaxis frequency fell 26.5% on 30 mg and 27.8% on 40 mg, against 18.0% on placebo. Duration fell 29.9% and 41.4%, against 23.8%. The effect was real, and the placebo response was high, which is exactly the pattern a Phase 3 must beat.
Safety stayed clean. Serious adverse events were similar across all three arms. The main on-target effects were mild-to-moderate rash, seen in 21% of the 30 mg group, 42% of the 40 mg group and 8% of placebo, plus reversible hyperglycemia in a handful of patients at the higher dose.
The round, and the names on the cap table
The Series B was oversubscribed and came with a specific purpose: fund the company through regulatory submissions and a potential U.S. approval of engasertib. That is runway framing, not a guarantee. No filing has been made and no PDUFA date exists.
Life Sciences at Goldman Sachs Alternatives and TCGX co-led, with Omega Funds, EQT Life Sciences, Perceptive and Kalehua Capital joining existing investors Medicxi and Droia. Medicxi co-founder Giovanni Mariggi takes a board seat alongside Goldman's Colin Walsh, TCGX's Giuliano Marostica and Omega's Francesco Draetta.
For a company that runs lean, the size of the round matters. The proceeds buy years of clinical operations, manufacturing scale-up and the regulatory conversation that a first-in-disease asset requires.
HEROIC, the trial that will decide
HEROIC is a global, randomized, double-blind, placebo-controlled Phase 3 study in patients with moderate-to-severe HHT. Sites are planned across North America, South America and Europe, and the principal investigator is Hanny Al-Samkari of Harvard Medical School and Mass General Brigham Cancer Institute.
The company has not disclosed target enrollment, primary endpoints in detail, or a topline readout date. What is disclosed is the structure: a placebo-controlled registrational program in a disease where no placebo-controlled drug has ever won.
What could still go wrong
The evidence so far is encouraging, and the history of rare-disease drug development argues for caution. Three specific risks stand out.
The placebo response is the first enemy
The rash rate is not trivial
Enrollment across three continents is slow by design
There is also the company's own history to weight. As we wrote in August, Ratio Therapeutics raised $70 million for an actinium-225 payload aimed at sarcoma, a different rare disease with a different mechanism, but the same structural bet: that a precise molecule can own a small, underserved market. Those bets are never safe until the data says so.
The field is forming behind it
Vaderis is not alone. Cure HHT, the patient advocacy group, now lists the company as a Clinical Trial Network partner alongside two others. Diagonal Therapeutics launched with $128 million and is dosing patients in a Phase 1 study of DIAG723, a bispecific designed to restore ALK1 signaling. Atavistik Bio began a Phase 1/2 trial of ATV-1601, an oral allosteric AKT1-selective inhibitor, in partnership with the Cure HHT network.
Vaderis's CEO puts it plainly: the company is proud to be in the lead, and pleased the others are coming in. More programs mean more optionality for patients, and more attention on a market that has been invisible to pharma for decades.
What would make engasertib the first approved HHT therapy?
Probability: 45%. The mechanism has already moved a placebo-controlled signal, the field is sparse, and a single successful registrational trial plus a modest safety package is enough for a first-in-disease approval.
✅ Arguments for
+ No approved therapy means no standard-of-care comparator to beat
+ $152 million funds the full registrational path, taking capital risk off the table
Confirmation criteria: HEROIC hits on epistaxis endpoints with a favorable safety profile in the 2028-2029 readout.
❌ Arguments against
− The 42% rash rate at the higher dose raises an adherence question regulators will probe
− Phase 2 to Phase 3 is where rare-disease programs most often fail
Disconfirmation criteria: HEROIC misses on primary endpoints, or safety signals worsen with longer exposure.
HEROIC enrollment milestones, once disclosed, tell you the trial is real and moving
Any Fast Track or breakthrough designation from the FDA would compress the approval timeline
Phase 1/2 data from Atavistik and Diagonal, which would test whether the whole AKT mechanism is durable
A disclosed readout date, which converts the story from thesis to schedule
Development scenarios
🟢 Optimistic scenario (25%)
Implications: The company becomes an acquisition target for pharma building a rare-vascular franchise.
🟡 Base-case scenario (55%)
Implications: A commercial first-mover in a 1-in-3,800 market with durable pricing power and a permanent innovation position.
🔴 Pessimistic scenario (20%)
Implications: The $152 million converts into a lesson about the distance between proof-of-concept and registration.
