Pheast Therapeutics

Pheast Therapeutics is an immuno-oncology company developing therapies that activate the innate immune system, specifically macrophages, against solid tumors. Its scientific premise is that cancer cells evade macrophage-mediated phagocytosis by expressing checkpoint or "don't eat me" signals; Pheast develops antibodies that block these signals so that tumor-infiltrating macrophages detect, engulf, and kill cancer cells. The company's founding discovery, published in Nature in 2019 (Barkal et al.), identified CD24 as a macrophage checkpoint acting through the inhibitory receptor Siglec-10, with high CD24 expression observed in ovarian and breast cancers.

The lead program, PHST001, is a humanized anti-CD24 IgG4 monoclonal antibody engineered to bind all glyco-variants of CD24 and to block the CD24–Siglec-10 interaction. Pheast describes CD24 as a potential advantage over prior macrophage checkpoint targets because it is not expressed on red blood cells and platelets, cell types that created safety challenges for other approaches. PHST001 entered a multicenter, open-label Phase 1 study in adults with advanced relapsed and/or refractory solid tumors (NCT06840886), planned to enroll up to 80 patients, with primary objectives of safety, tolerability, and establishing a recommended Phase 2 dose, and secondary endpoints covering pharmacokinetics and early anti-tumor activity. Company communications describe advancement into Phase 1b combination cohorts in 2026 and initial Phase 1a data presented at AACR 2026.

Beyond PHST001, the pipeline includes PHST677, a bispecific antibody-drug conjugate targeting CDH1 and Nectin-4 (IND-enabling), an undisclosed program PHST002 (IND-enabling), and PHST004 (discovery). Pheast states it applies the same genetic and molecular screening technologies used to find CD24 to identify additional macrophage checkpoints and tumor-specific antigens, including approaches adding cytotoxic payloads, and is exploring macrophage-directed approaches in inflammation indications beyond oncology.

Founding story

The foundational research originated in Irv Weissman's laboratory at the Stanford University Institute for Stem Cell Biology and Regenerative Medicine, where the cofounders met and trained. Amira Barkal, working on her doctoral thesis in the Weissman lab, identified CD24 as a macrophage checkpoint signaling through Siglec-10, published in Nature in 2019. Pheast was founded in 2020 as a spinout of the Weissman lab by Barkal, Weissman, Ravi Majeti, and Roy Maute.

Business model

Pheast is a therapeutics developer that discovers and advances proprietary antibody candidates through preclinical and clinical development; it is venture-funded and has no disclosed commercial products or revenue.

Traction

PHST001 is in a Phase 1 multicenter, open-label study (NCT06840886) enrolling up to 80 patients with advanced relapsed and/or refractory solid tumors; the first patient was treated in April 2025 and the trial was actively recruiting as of June 2025. FDA Fast Track designation was granted in June 2025 for platinum-resistant ovarian cancer and, in combination with chemotherapy, platinum-sensitive ovarian cancer. Three additional programs (PHST677, PHST002, PHST004) are in IND-enabling or discovery stages. The company has presented at AACR, ASCO, SITC, AACR-NCI-EORTC, and PEGS Boston, and published in Nature (2019) and Clinical Cancer Research (2026).

Latest developments

In 2026, Pheast reported advancing PHST001 into Phase 1b combination cohorts (March 2026), presented initial Phase 1a clinical data and preclinical studies at AACR 2026 (April 2026), presented preclinical data on the bispecific ADC PHST677 at the PEGS Boston Summit (May 2026), announced a Clinical Cancer Research publication on PHST001 anti-tumor activity (July 2026), and hosted a KOL webinar on macrophage checkpoint biology (August 2026).