EcoR1 Capital, LLC

EcoR1 Capital's $2.36B portfolio as of March 31, 2026 is almost entirely a single-asset-class bet: every top position is a clinical-stage or platform biotechnology company, and four names alone consume 67% of the book. Zymeworks (ZYME) leads at 24.4% ($575M), followed by AnaptysBio (ANAB) at 18.5% ($437M), Jazz Pharmaceuticals (JAZZ) at 13.7% ($323M), and Centessa Pharmaceuticals (CNTA) at 10.8% ($255M). The fund added $86M of Zymeworks in Q1 and more than doubled its Centessa stake to $255M — a $177M increase that made Centessa the portfolio's fastest-growing position in dollar terms. The rotation within biotech leaned into antibody engineering and oncology: AKTIS Oncology ($86M), Oric Pharmaceuticals ($85M), CG Oncology ($75M), Eton Pharmaceuticals ($54M), and Relay Therapeutics ($19M) all entered the book in the quarter, while Immunome, Structure Therapeutics, Vaxcyte, and Atara Biotherapeutics were exited entirely. The result is a portfolio with 62 named positions that functions as a concentrated thematic bet on late-stage oncology and protein-engineering platforms — any clinical-trial disappointment in the top holdings would compress the portfolio disproportionately. The whaleScore of 79.75 reflects the sheer size of the book rather than diversification; EcoR1 has built one of the largest single-manager biotech portfolios on record, and its Q1 2026 filing documents an even deeper commitment to that lane.