13F Pro

SEC Form 4 reporting owner

EcoR1 Capital, LLC

EcoR1 Capital, LLC has filed 14 Form 4 transactions reported between January 12, 2026 and May 7, 2026, as 10% owner of Atara Biotherapeutics, Inc., 10% owner of First Tracks Biotherapeutics, Inc. and Director of Aktis Oncology, Inc..

Name as filed: EcoR1 Capital, LLC

Open-market buys, 24 mo
$44.7M
3 lines
Open-market sales, 24 mo
$65.0M
1 lines
Companies
3
with Form 4 filings
Latest transaction
May 7, 2026
transaction date

Roles and reported holdings

  • ATRAAtara Biotherapeutics, Inc.
    May 7, 2026

    10% owner

    Held indirectly (latest line)1,552,000 sh as of May 7, 2026 · Form 4

    24 months: $4.7M bought

  • TRAXFirst Tracks Biotherapeutics, Inc.
    Apr 20, 2026

    10% owner

    Held indirectly (latest line)3,174,519 sh as of Apr 20, 2026 · Form 4

    24 months: $65.0M sold

  • AKTSAktis Oncology, Inc.
    Jan 12, 2026

    Director

    Held indirectly (latest line)347,305 sh as of Jan 12, 2026 · Form 4

    24 months: $40.0M bought

Transaction history

All 14 reported transactions, newest first. Every row links to the Form 4 on SEC EDGAR.

DateCompanyTypeSharesValueFiling
May 7, 2026ATRA10% ownerOpen-market purchaseCode P · indirect507,407$4.7M@ $9.35Form 4
Apr 20, 2026TRAX10% ownerOpen-market saleCode S · indirect4,705,575$65.0M@ $13.81Form 4
Jan 12, 2026AKTSDirectorConversion of derivativeCode C · indirect86,222—Form 4
Jan 12, 2026AKTSDirectorConversion of derivativeCode C · indirect965,190—Form 4
Jan 12, 2026AKTSDirectorConversion of derivativeCode C · indirect102,500—Form 4
Jan 12, 2026AKTSDirectorConversion of derivativeCode C · indirect2,397,500—Form 4
Jan 12, 2026AKTSDirectorConversion of derivativeCode C · indirect488,891—Form 4
Jan 12, 2026AKTSDirectorConversion of derivativeCode C · indirect997,299—Form 4
Jan 12, 2026AKTSDirectorConversion of derivativeCode C · indirect9,913,810—Form 4
Jan 12, 2026AKTSDirectorOpen-market purchaseCode P · indirect144,443$2.6M@ $18.00Form 4
Jan 12, 2026AKTSDirectorOpen-market purchaseCode P · indirect2,077,779$37.4M@ $18.00Form 4
Jan 12, 2026AKTSDirectorConversion of derivativeCode C · indirect128,506—Form 4
Jan 12, 2026AKTSDirectorConversion of derivativeCode C · indirect202,862—Form 4
Jan 12, 2026AKTSDirectorConversion of derivativeCode C · indirect2,270,879—Form 4

How this page is built

Every row comes from a Form 4 filed with the SEC, which officers, directors and holders of more than 10% of a company’s stock must file within two business days of a trade. Transactions are grouped by the reporting owner’s name as filed (spacing, capitals and punctuation ignored); two different people filing under an identical name would appear together, and one person filing under two spellings appears on two pages.

Open-market totals count code P purchases and code S sales over the last 24 months. The same trade reported on more than one filing is counted once; when another owner (for example a fund and its general partner) reports the identical trade, they are listed beside it. Holdings are the shares owned after the latest purchase, sale, gift or tax-withholding line, shown separately for direct and indirect ownership; an indirect figure is one holding line, not a total across every trust or entity.

This page describes what was filed with the SEC; it is not investment advice or a recommendation to buy or sell any security.