EcoR1 Capital, LLC 13F: Quarter-over-Quarter Portfolio Changes
EcoR1 Capital, LLC reported a disclosed portfolio value of approximately $2.3 billion in its latest SEC Form 13F-HR filing for Q1 2026, up 6.8% quarter on quarter. Over the quarter, the fund initiated 10 new positions, bought more shares in 4 holdings, trimmed 4 holdings, and exited 9 positions.
EcoR1 Capital, LLC's top buy was Centessa Pharmaceuticals PLC (CNTA) . The fund bought 92.6% more shares, lifting the position's portfolio weight by 6.6 percentage points. Its top sell was Immunome INC (IMNM) . The fund exited the position completely after it had accounted for 2.8% of the previous portfolio.
New PositionsQ1 2026
Securities disclosed for the first time in Q1 2026 that were not present in the prior 13F-HR filing.
| Company | Ticker | Initial Portfolio Weight | History |
|---|---|---|---|
| AKTIS ONCOLOGY INC | AKTS | 3.7% | History → |
| RELAY THERAPEUTICS INC | RLAY | 0.8% | Holders → |
| ERASCA INC | ERAS | 0.6% | Holders → |
| EIKON THERAPEUTICS INC | EIKN | 0.3% | Holders → |
| REPLIMUNE GROUP INC | REPL | 0.3% | Holders → |
| ZURA BIO LTD | ZURA | 0.3% | Holders → |
| PHATHOM PHARMACEUTICALS INC | PHAT | 0.3% | Holders → |
| STOKE THERAPEUTICS INC | STOK | 0.1% | Holders → |
| PRELUDE THERAPEUTICS INC | PRLD | 0.1% | Holders → |
| HELIX ACQUISITION CORP III | HLXC | 0.1% | Holders → |
Top BuysQ1 2026
The fund's top buys among existing positions in Q1 2026. Ranked by portfolio-weight impact, with the percentage of additional shares shown separately.
| Company | Ticker | Portfolio Weight Change | More Shares | History |
|---|---|---|---|---|
| CENTESSA PHARMACEUTICALS PLC | CNTA | +6.6% | +92.6% | History → |
| MEREO BIOPHARMA GROUP PLC | MREO | +0.0% | +70.2% | Holders → |
| CG ONCOLOGY INC | CGON | +1.7% | +42.7% | History → |
| ETON PHARMACEUTICALS INC | ETON | +0.7% | +7.0% | History → |
Top SellsQ1 2026
The fund's top sells among positions it retained in Q1 2026. Ranked by portfolio-weight impact. Full exits are listed separately.
| Company | Ticker | Portfolio Weight Change | Shares Sold | History |
|---|---|---|---|---|
| ATARA BIOTHERAPEUTICS INC | ATRA | -0.5% | 82.6% | Holders → |
| MBX BIOSCIENCES INC | MBX | -2.1% | 63.4% | Holders → |
| XENCOR INC | XNCR | -1.1% | 32.9% | Holders → |
| IBIO INC | IBIO | -0.1% | 28.9% | Holders → |
Full ExitsQ1 2026
Positions present in the prior 13F-HR filing that no longer appear in Q1 2026.
| Company | Ticker | Last-Reported Portfolio Weight |
|---|---|---|
| IMMUNOME INC | IMNM | 2.8% |
| STRUCTURE THERAPEUTICS INC | GPCR | 1.1% |
| VAXCYTE INC | PCVX | 0.9% |
| AQUESTIVE THERAPEUTICS INC | AQST | 0.8% |
| VOYAGER THERAPEUTICS INC | VYGR | 0.7% |
| MANNKIND CORP | MNKD | 0.4% |
| NUVATION BIO INC | NUVB/WS | 0.4% |
| EVOLUS INC | EOLS | 0.2% |
| CAMP4 THERAPEUTICS CORP | CAMP | 0.1% |
Net Portfolio Value ChangeQ1 2026
- $2.2BPrior quarter
- $2.3BCurrent quarter
- +$0.1BNet delta
- +6.8%% change
Methodology & FAQ
How EcoR1 Capital, LLC Quarterly Changes Are Computed
All deltas are sourced from sequential SEC Form 13F-HR filings for EcoR1 Capital, LLC: each row joins the most recent filing against the immediately preceding quarterly filing for the same fund. Share-count changes reflect reported trading activity, while portfolio weights can also move because of market price changes. Portfolio weights are normalized to exclude listed options for comparability. A complete description — including how confidential treatment filings are handled — is documented in the Methodology.
What stocks did EcoR1 Capital, LLC buy in Q1 2026?
In Q1 2026, EcoR1 Capital, LLC initiated 10 new positions (AKTIS ONCOLOGY INC (AKTS), RELAY THERAPEUTICS INC (RLAY), ERASCA INC (ERAS), EIKON THERAPEUTICS INC (EIKN), REPLIMUNE GROUP INC (REPL), ZURA BIO LTD (ZURA), PHATHOM PHARMACEUTICALS INC (PHAT), STOKE THERAPEUTICS INC (STOK), PRELUDE THERAPEUTICS INC (PRLD), HELIX ACQUISITION CORP III (HLXC)); bought more shares of CENTESSA PHARMACEUTICALS PLC (CNTA), MEREO BIOPHARMA GROUP PLC (MREO), CG ONCOLOGY INC (CGON), ETON PHARMACEUTICALS INC (ETON).
What stocks did EcoR1 Capital, LLC sell in Q1 2026?
In Q1 2026, EcoR1 Capital, LLC fully sold 9 positions (IMMUNOME INC (IMNM), STRUCTURE THERAPEUTICS INC (GPCR), VAXCYTE INC (PCVX), AQUESTIVE THERAPEUTICS INC (AQST), VOYAGER THERAPEUTICS INC (VYGR), MANNKIND CORP (MNKD), NUVATION BIO INC (NUVB/WS), EVOLUS INC (EOLS), CAMP4 THERAPEUTICS CORP (CAMP)); reduced holdings in ATARA BIOTHERAPEUTICS INC (ATRA), MBX BIOSCIENCES INC (MBX), XENCOR INC (XNCR), IBIO INC (IBIO).
Which positions did EcoR1 Capital, LLC initiate in Q1 2026?
EcoR1 Capital, LLC established 10 new positions in Q1 2026: AKTIS ONCOLOGY INC (AKTS, 3.7%), RELAY THERAPEUTICS INC (RLAY, 0.8%), ERASCA INC (ERAS, 0.6%), EIKON THERAPEUTICS INC (EIKN, 0.3%), REPLIMUNE GROUP INC (REPL, 0.3%), ZURA BIO LTD (ZURA, 0.3%), PHATHOM PHARMACEUTICALS INC (PHAT, 0.3%), STOKE THERAPEUTICS INC (STOK, 0.1%), PRELUDE THERAPEUTICS INC (PRLD, 0.1%), HELIX ACQUISITION CORP III (HLXC, 0.1%).
Which existing positions saw the largest allocation increases for EcoR1 Capital, LLC in Q1 2026?
Of 4 existing positions with share-count increases in Q1 2026, the largest were: CENTESSA PHARMACEUTICALS PLC (CNTA, +6.6% weight, +92.6% shares), MEREO BIOPHARMA GROUP PLC (MREO, +0.0% weight, +70.2% shares), CG ONCOLOGY INC (CGON, +1.7% weight, +42.7% shares), ETON PHARMACEUTICALS INC (ETON, +0.7% weight, +7.0% shares).
Which positions did EcoR1 Capital, LLC fully exit in Q1 2026?
EcoR1 Capital, LLC fully exited 9 positions in Q1 2026: IMMUNOME INC (IMNM, last-reported weight 2.8%), STRUCTURE THERAPEUTICS INC (GPCR, last-reported weight 1.1%), VAXCYTE INC (PCVX, last-reported weight 0.9%), AQUESTIVE THERAPEUTICS INC (AQST, last-reported weight 0.8%), VOYAGER THERAPEUTICS INC (VYGR, last-reported weight 0.7%), MANNKIND CORP (MNKD, last-reported weight 0.4%), NUVATION BIO INC (NUVB/WS, last-reported weight 0.4%), EVOLUS INC (EOLS, last-reported weight 0.2%), CAMP4 THERAPEUTICS CORP (CAMP, last-reported weight 0.1%).
Which existing positions saw the largest allocation reductions for EcoR1 Capital, LLC in Q1 2026?
Of 4 existing positions with share-count reductions in Q1 2026, the largest were: ATARA BIOTHERAPEUTICS INC (ATRA, -0.5% weight, -82.6% shares), MBX BIOSCIENCES INC (MBX, -2.1% weight, -63.4% shares), XENCOR INC (XNCR, -1.1% weight, -32.9% shares), IBIO INC (IBIO, -0.1% weight, -28.9% shares).
Do quarter-over-quarter 13F allocation changes constitute explicit trading signals?
No. Quarter-over-quarter changes reflect a combination of active trading and market price movement. A weight increase can result from price appreciation alone, without the manager adding shares. Share-count delta is the cleaner indicator of explicit trading activity. All deltas on this page are sourced from sequential SEC Form 13F-HR filings.