ATRA SEC Filing News — Atara Biotherapeutics, Inc.

Latest SEC filings for Atara Biotherapeutics, Inc. (ATRA) explained in plain English. Covers insider buying and selling (Form 4), proposed insider sales (Form 144), material company events (8-K), and quarterly & annual reports (10-Q / 10-K). StrongBuyAnalytics provides navigation and brief excerpts or summaries; original filings remain at the SEC/source links and were authored by their filers, not StrongBuyAnalytics. Filing dates shown are source dates. Coverage and detection can be delayed or incomplete because of SEC availability, amendments, parsing, caching, or outages. Latest source filing date shown: 2026-09-04.

Atara Biotherapeutics, Inc. engages in the development of transformative therapies for patients with cancer and autoimmune disease in the United States and internationally. Its lead product includes Tab-cel (tabelecleucel), a T-cell immunotherapy program that is in Phase 3 clinical trials for the treatment of epstein-barr virus (EBV) with post-transplant lymphoproliferative disease, as well as other EBV-driven diseases. It also develops ATA3219, an allogeneic CAR T targeting CD19 intended to tar…
Sector: Healthcare Industry: Biotechnology Market Cap: $93.9M
20
Total Filings
2
Bullish Classifications
4
Bearish Classifications
11
Insider Transactions
4
Material Events (8-K)
2
Periodic Reports
Rule-based classifications for ATRA currently lean bearish. Of the 20 filing records displayed, 4 carry bearish classifications (such as insider sales or negative 8-K disclosures) versus 2 bullish. This does not necessarily signal fundamental deterioration — insiders sell for many reasons — but it is worth monitoring alongside the company's core financial metrics.
ATRA Filing Activity Snapshot 2026-05-11 — 2026-09-04
Insider Transactions (Form 4)
2 buys vs 4 sells
Net insider selling in this period — insiders sell for many reasons beyond conviction.
Largest Form 144 Filing
$4.74M
EcoR1 Capital, LLC (10% Owner) · 2026-05-11
507,407 shares · Form 4
Form 144 Notices
3
Proposed insider sales filed — Form 144 is a notice of intent, not a confirmed transaction. Actual sales are confirmed via Form 4.
Insider Transactions 11 · Forms 3, 4 and 5

A Form 4 is filed within two business days of a company insider — an officer, a director, or a holder of more than ten percent of the stock — changing their position in the shares. All 11 filings in this group are Form 4s for Atara Biotherapeutics, Inc.

The difficulty with reading these filings as a group is that a single form type covers transactions that mean entirely different things. An executive spending their own money to buy stock and an executive having shares withheld to pay tax on a vesting grant both appear as a Form 4. Every filing below is therefore tagged with the nature of the underlying transaction, taken from the transaction code reported on the form itself.

Across the 11 insider filings shown, the breakdown is 4 compensation award, 4 open-market sale, 2 open-market purchase and 1 option exercise. 6 of them involved a discretionary open-market trade; the rest are compensation and administrative mechanics.

What each transaction type means

Compensation award ×4
Shares were granted as compensation rather than purchased. No cash changed hands, so the filing reflects a pay decision by the company, not a judgement about the price.
Open-market sale ×4
The insider sold shares on the open market. Sales may be discretionary or executed automatically under a pre-arranged Rule 10b5-1 trading plan, and a Form 4 does not always make clear which applies.
Open-market purchase ×2
The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.
Option exercise ×1
The insider converted options into shares. The exercise price was fixed when the options were granted, so the timing usually tracks an expiry schedule.
Form 4 Open-market purchase Insider Buying 2026-09-04

ATRA insider Cherry Brian N (Director) bought 104,166 shares (~$1000.0K)

Cherry Brian N, listed as Director at Atara Biotherapeutics, Inc., reported an open-market purchase of 104,166 ATRA shares in a Form 4 filing. Insider buying is often treated as a bullish signal because company insiders are committing their own capital.

The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.

Transactions reported on this filing
Code Nature Shares Price Value
P Open-market purchase 104,166 $9.60 $1000.0K
Filing: Form 4 (Insider Transaction) Insider: Cherry Brian N (Director) Shares: 104,166 Est. Value: $1000.0K
View on SEC EDGAR → Open Filing Document →
Form 4 Open-market sale Insider Selling 2026-08-26

ATRA insider Nguyen AnhCo (Director, President and CEO) sold 5,062 shares (~$40.9K)

Nguyen AnhCo, listed as Director, President and CEO at Atara Biotherapeutics, Inc., reported an open-market sale of 5,062 ATRA shares in a Form 4 filing. This is a confirmed insider sale, not just a proposed sale notice.

The insider sold shares on the open market. Sales may be discretionary or executed automatically under a pre-arranged Rule 10b5-1 trading plan, and a Form 4 does not always make clear which applies.

Transactions reported on this filing
Code Nature Shares Price Value
S Open-market sale 5,062 $8.08 $40.9K
Filing: Form 4 (Insider Transaction) Insider: Nguyen AnhCo (Director, President and CEO) Shares: 5,062 Est. Value: $40.9K
View on SEC EDGAR → Open Filing Document →
Form 4 Option exercise Tax / Compensation Filing 2026-07-24

ATRA insider Form 4 filed for equity award, exercise, or tax withholding

Redmile Group, LLC (Director) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

The insider converted options into shares. The exercise price was fixed when the options were granted, so the timing usually tracks an expiry schedule.

Transactions reported on this filing
Code Nature Shares Price Value
M Option exercise 195,211 — —
F Tax withholding on vested shares 60 — —
M Option exercise derivative · Pre-Funded Warrants to Purchase Common Stock 101,089 — —
M Option exercise derivative · Pre-Funded Warrants to Purchase Common Stock 38,735 — —
M Option exercise derivative · Pre-Funded Warrants to Purchase Common Stock 55,387 — —
Filing: Form 4 (Insider Transaction) Insider: Redmile Group, LLC (Director) Shares: 195,271
View on SEC EDGAR → Open Filing Document →
Form 4 Compensation award Tax / Compensation Filing 2026-06-15

ATRA insider Form 4 filed for equity award, exercise, or tax withholding

Cherry Brian N (Director) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

Shares were granted as compensation rather than purchased. No cash changed hands, so the filing reflects a pay decision by the company, not a judgement about the price.

Transactions reported on this filing
Code Nature Shares Price Value
A Compensation award 24,000 — —
Filing: Form 4 (Insider Transaction) Insider: Cherry Brian N (Director) Shares: 24,000
View on SEC EDGAR → Open Filing Document →
Form 4 Compensation award Tax / Compensation Filing 2026-06-11

ATRA insider Form 4 filed for equity award, exercise, or tax withholding

HEIDEN WILLIAM K (Director) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

Shares were granted as compensation rather than purchased. No cash changed hands, so the filing reflects a pay decision by the company, not a judgement about the price.

Transactions reported on this filing
Code Nature Shares Price Value
A Compensation award 12,000 — —
Filing: Form 4 (Insider Transaction) Insider: HEIDEN WILLIAM K (Director) Shares: 12,000
View on SEC EDGAR → Open Filing Document →
Form 4 Compensation award Tax / Compensation Filing 2026-06-11

ATRA insider Form 4 filed for equity award, exercise, or tax withholding

Fust Matthew K (Director) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

Shares were granted as compensation rather than purchased. No cash changed hands, so the filing reflects a pay decision by the company, not a judgement about the price.

Transactions reported on this filing
Code Nature Shares Price Value
A Compensation award 12,000 — —
Filing: Form 4 (Insider Transaction) Insider: Fust Matthew K (Director) Shares: 12,000
View on SEC EDGAR → Open Filing Document →
Form 4 Compensation award Tax / Compensation Filing 2026-06-11

ATRA insider Form 4 filed for equity award, exercise, or tax withholding

Ciongoli Gregory Austin (Director, 10% Owner) filed a Form 4 covering compensation-related activity such as stock awards, option exercises, conversions, or tax withholding. These filings are usually neutral.

Shares were granted as compensation rather than purchased. No cash changed hands, so the filing reflects a pay decision by the company, not a judgement about the price.

Transactions reported on this filing
Code Nature Shares Price Value
A Compensation award 12,000 — —
Filing: Form 4 (Insider Transaction) Insider: Ciongoli Gregory Austin (Director, 10% Owner) Shares: 12,000
View on SEC EDGAR → Open Filing Document →
Form 4 Open-market sale Insider Selling 2026-05-20

ATRA insider Nguyen AnhCo (Director, President and CEO) sold 5,241 shares (~$47.8K)

Nguyen AnhCo, listed as Director, President and CEO at Atara Biotherapeutics, Inc., reported an open-market sale of 5,241 ATRA shares in a Form 4 filing. This is a confirmed insider sale, not just a proposed sale notice.

The insider sold shares on the open market. Sales may be discretionary or executed automatically under a pre-arranged Rule 10b5-1 trading plan, and a Form 4 does not always make clear which applies.

Transactions reported on this filing
Code Nature Shares Price Value
S Open-market sale 5,241 $9.13 $47.8K
Filing: Form 4 (Insider Transaction) Insider: Nguyen AnhCo (Director, President and CEO) Shares: 5,241 Est. Value: $47.8K
View on SEC EDGAR → Open Filing Document →
Form 4 Open-market sale Insider Selling 2026-05-20

ATRA insider Grant-Huerta Yanina (Chief Accounting Officer) sold 2,414 shares (~$22.0K)

Grant-Huerta Yanina, listed as Chief Accounting Officer at Atara Biotherapeutics, Inc., reported an open-market sale of 2,414 ATRA shares in a Form 4 filing. This is a confirmed insider sale, not just a proposed sale notice.

The insider sold shares on the open market. Sales may be discretionary or executed automatically under a pre-arranged Rule 10b5-1 trading plan, and a Form 4 does not always make clear which applies.

Transactions reported on this filing
Code Nature Shares Price Value
S Open-market sale 2,414 $9.13 $22.0K
Filing: Form 4 (Insider Transaction) Insider: Grant-Huerta Yanina (Chief Accounting Officer) Shares: 2,414 Est. Value: $22.0K
View on SEC EDGAR → Open Filing Document →
Form 4 Open-market sale Insider Selling 2026-05-11

ATRA insider Panacea Innovation Ltd (10% Owner) sold 313,446 shares (~$3.17M)

Panacea Innovation Ltd, listed as 10% Owner at Atara Biotherapeutics, Inc., reported an open-market sale of 313,446 ATRA shares in a Form 4 filing. This is a confirmed insider sale, not just a proposed sale notice.

The insider sold shares on the open market. Sales may be discretionary or executed automatically under a pre-arranged Rule 10b5-1 trading plan, and a Form 4 does not always make clear which applies.

Transactions reported on this filing
Code Nature Shares Price Value
S Open-market sale 313,446 $10.10 $3.17M
Filing: Form 4 (Insider Transaction) Insider: Panacea Innovation Ltd (10% Owner) Shares: 313,446 Est. Value: $3.17M
View on SEC EDGAR → Open Filing Document →
Form 4 Open-market purchase Insider Buying 2026-05-11

ATRA insider EcoR1 Capital, LLC (10% Owner) bought 507,407 shares (~$4.74M)

EcoR1 Capital, LLC, listed as 10% Owner at Atara Biotherapeutics, Inc., reported an open-market purchase of 507,407 ATRA shares in a Form 4 filing. Insider buying is often treated as a bullish signal because company insiders are committing their own capital.

The insider bought shares on the open market with their own money. This is the only Form 4 category that requires a discretionary cash outlay at the prevailing price.

Transactions reported on this filing
Code Nature Shares Price Value
P Open-market purchase 507,407 $9.35 $4.74M
Filing: Form 4 (Insider Transaction) Insider: EcoR1 Capital, LLC (10% Owner) Shares: 507,407 Est. Value: $4.74M
View on SEC EDGAR → Open Filing Document →
Proposed Insider Sales 3 · Form 144

A Form 144 is a notice of intent to sell restricted or control securities. It is not a record that anything was sold. Atara Biotherapeutics, Inc. has 3 such notices in this period.

The distinction matters because a Form 144 is frequently reported as though it were a completed insider sale. The filer may sell all of the shares covered, some of them, or none at all, and there is no obligation to update the notice either way. A sale that is actually executed by an officer or director shows up separately on a Form 4, which is the filing to check before treating a proposed sale as a real one.

Form 144 Proposed Insider Sale 2026-08-26

ATRA Form 144 filed for proposed insider sale by Nguyen AnhCo (5,062 shares) ~$42.3K

Nguyen AnhCo filed a Form 144 with the SEC indicating intent to sell ATRA (Atara Biotherapeutics, Inc.) shares. Form 144 reflects a proposed sale, not a completed transaction. The actual execution, if any, would typically appear later in a Form 4.

Filing: Form 144 (Proposed Sale Notice) Insider: Nguyen AnhCo Shares: 5,062 Est. Value: $42.3K
View on SEC EDGAR → Open Filing Document →
Form 144 Proposed Insider Sale 2026-05-18

ATRA Form 144 filed for proposed insider sale by Nguyen AnhCo (5,981 shares) ~$62.7K

Nguyen AnhCo filed a Form 144 with the SEC indicating intent to sell ATRA (Atara Biotherapeutics, Inc.) shares. Form 144 reflects a proposed sale, not a completed transaction. The actual execution, if any, would typically appear later in a Form 4.

Filing: Form 144 (Proposed Sale Notice) Insider: Nguyen AnhCo Shares: 5,981 Est. Value: $62.7K
View on SEC EDGAR → Open Filing Document →
Form 144 Proposed Insider Sale 2026-05-18

ATRA Form 144 filed for proposed insider sale by Grant-Huerta Yanina (2,754 shares) ~$28.9K

Grant-Huerta Yanina filed a Form 144 with the SEC indicating intent to sell ATRA (Atara Biotherapeutics, Inc.) shares. Form 144 reflects a proposed sale, not a completed transaction. The actual execution, if any, would typically appear later in a Form 4.

Filing: Form 144 (Proposed Sale Notice) Insider: Grant-Huerta Yanina Shares: 2,754 Est. Value: $28.9K
View on SEC EDGAR → Open Filing Document →
Material Events 4 · Form 8-K

An 8-K reports a material event in the window between scheduled reports. There are 4 in this period for Atara Biotherapeutics, Inc. Each 8-K names the item number it is filed under, and that number is the fastest way to tell a routine disclosure from a consequential one.

Item 2.02 is an earnings release, Item 5.02 is a change of directors or officers, and Item 1.01 or 2.01 covers a material agreement or a completed acquisition. Item 7.01 and Item 8.01 are the general-purpose disclosure items and carry no fixed meaning on their own.

Form 8-K Material Company Update 2026-08-12

ATRA filed 8-K — material company event

Atara Biotherapeutics, Inc. filed an 8-K with the SEC reporting a material event. Summary unavailable — view the original SEC filing for the full text.

Filing: 8-K (Material Event)
View on SEC EDGAR → Open Filing Document →
Form 8-K Material Company Update 2026-06-26

ATRA filed 8-K — material company event

Atara Biotherapeutics, Inc. filed an 8-K with the SEC reporting a material event. Summary unavailable — view the original SEC filing for the full text.

Filing: 8-K (Material Event)
View on SEC EDGAR → Open Filing Document →
Form 8-K Material Company Update 2026-06-12

ATRA filed 8-K — material company event

Atara Biotherapeutics, Inc. filed an 8-K with the SEC reporting a material event. Summary unavailable — view the original SEC filing for the full text.

Filing: 8-K (Material Event)
View on SEC EDGAR → Open Filing Document →
Form 8-K Material Company Update 2026-05-12

ATRA filed 8-K — material company event

Atara Biotherapeutics, Inc. filed an 8-K with the SEC reporting a material event. Summary unavailable — view the original SEC filing for the full text.

Filing: 8-K (Material Event)
View on SEC EDGAR → Open Filing Document →
Periodic Reports 2 · Forms 10-K and 10-Q

The periodic reports are where the audited and reviewed financial statements live. This period contains 2 quarterly reports (10-Q) for Atara Biotherapeutics, Inc.

The two are not equivalent in weight. A 10-K is audited by an external firm and includes the full risk factor disclosure, business description and management discussion; a 10-Q is unaudited, reviewed rather than examined, and much shorter. When a figure in a quarterly report is later revised, the annual report is usually where the correction appears.

An amended report — 10-K/A or 10-Q/A — restates or corrects something in the original filing, and is worth reading against the version it replaces.

Form 10-Q Quarterly Report 2026-08-12

ATRA filed Quarterly Report (10-Q)

Atara Biotherapeutics, Inc. filed its quarterly report with the SEC. This report includes unaudited financial statements and management discussion for the quarter.

Filing: 10-Q (Quarterly Report)
View on SEC EDGAR → Open Filing Document →
Form 10-Q Quarterly Report 2026-05-12

ATRA filed Quarterly Report (10-Q)

Atara Biotherapeutics, Inc. filed its quarterly report with the SEC. This report includes unaudited financial statements and management discussion for the quarter.

Filing: 10-Q (Quarterly Report)
View on SEC EDGAR → Open Filing Document →

How we classify Atara Biotherapeutics, Inc.'s filings

Straight from EDGAR

Each displayed record links to an original source document. StrongBuyAnalytics provides navigation and brief excerpts or summaries, not the filing itself. Parsing may omit context or contain errors, so read the original document in full.

Transaction codes, not guesswork

The nature shown on each insider filing comes from the transaction code the filer entered on the form itself — P for an open-market purchase, A for a compensation award, F for shares withheld to pay tax, M for an option exercise. Where one filing contains several codes, the transaction table lists them line by line.

Why the distinction matters

Insider activity is routinely summarised as buying or selling, which flattens together decisions that mean very different things. Shares withheld for tax on a vesting grant are an automatic administrative step; shares bought on the open market are someone committing their own money at the current price.

What this page does not tell you

A filing records what happened, not why. Form 4 does not always disclose whether a sale was executed under a pre-arranged Rule 10b5-1 plan, and no single filing is a basis for a decision on ATRA. Read these alongside the fundamentals rather than in isolation.

Frequently Asked Questions — ATRA SEC Filings

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Publisher, sources & limitations — September 15, 2026. StrongBuyAnalytics provides navigation and brief excerpts or summaries for educational use. Original filings remain at SEC EDGAR or other displayed source links; StrongBuyAnalytics does not author them. Filing dates are source dates, not publication dates for this page. Coverage can be delayed, incomplete, amended, or unavailable because of SEC/source availability, parsing, caching, or outages. Verify every material statement in the original filing.
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