Form 10-12B/A Atrium Therapeutics,

As filed with the Securities and Exchange Commission on January 29, 2026

File No. 001-43008

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Amendment No. 1

to

FORM 10

GENERAL FORM FOR REGISTRATION OF SECURITIES

Pursuant to Section 12(b) or (g) of

The Securities Exchange Act of 1934

Atrium Therapeutics, Inc.

(Exact name of registrant as specified in its charter)

(619) 876-0700

(Registrant’s telephone number, including area code)

Securities to be registered pursuant to Section 12(b) of the Act:

Securities to be registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12(b)-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

INFORMATION REQUIRED IN REGISTRATION STATEMENT CROSS REFERENCE

SHEET BETWEEN ITEMS OF FORM 10 AND THE ATTACHED INFORMATION STATEMENT.

Certain information required to be included herein is incorporated by reference to specifically identified portions of the body of the information statement filed herewith as Exhibit 99.1 (the “Information Statement”). None of the information contained in the Information Statement shall be incorporated by reference herein or deemed to be a part hereof unless such information is specifically incorporated by reference.

The information required by this item is contained under the sections “Questions and Answers about the Separation and Distribution,” “Information Statement Summary,” “Cautionary Statement Regarding Forward-Looking Statements,” “Business,” and “Where You Can Find More Information” of the Information Statement. Those sections are incorporated herein by reference.

The information required by this item is contained under the sections “Information Statement Summary” and “Risk Factors” in the Information Statement. Those sections are incorporated herein by reference.

The information required by this item is contained under the sections “Capitalization,” “Unaudited Pro Forma Combined Financial Information,” “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and “Combined Financial Statements” of the Information Statement.

Those sections are incorporated herein by reference.

The information required by this item is contained under the section “Business—Properties” of the Information Statement. That section is incorporated herein by reference.

The information required by this item is contained under the section “Security Ownership of Certain Beneficial Owners and Management” of the Information Statement. That section is incorporated herein by reference.

The information required by this item is contained under the section “Corporate Governance and Management” of the Information Statement. That section is incorporated herein by reference.

The information required by this item is contained under the sections “Corporate Governance and Management—Non-Employee Director Compensation,” “Corporate Governance and Management—Human Capital Management Committee Interlocks and Insider Participation” and “Executive Compensation” of the Information Statement. Those sections are incorporated herein by reference.

The information required by this item is contained under the sections “Certain Relationships and Related Party Transactions,” “Security Ownership of Certain Beneficial Owners and Management” and “Corporate

Governance and Management—Director Independence” of the Information Statement. Those sections are incorporated herein by reference.

The information required by this item is contained under the section “Business—Legal Proceedings” of the Information Statement. That section is incorporated herein by reference.

The information required by this item is contained under the sections “Information Statement Summary,” “Risk Factors,” “The Separation and Distribution,” “Dividend Policy,” “Corporate Governance and Management,” “Shares Eligible for Future Sale” and “Description of Securities” of the Information Statement. Those sections are incorporated herein by reference.

None.

The information required by this item is contained under the sections “Questions and Answers about the Separation and Distribution,” “Information Statement Summary,” “The Separation and Distribution” and “Description of Securities” of the Information Statement. Those sections are incorporated herein by reference.

The information required by this item is contained under the sections “The Separation and Distribution—The Separation Agreement—Indemnification,” “Executive Compensation—Limitation of Liability and Indemnification of Officers and Directors,” “Certain Relationships and Related Party Transactions—Indemnification Agreements” and “Indemnification of Directors and Officers” of the Information Statement. Those sections are incorporated herein by reference.

The information required by this item is contained under the sections “Unaudited Pro Forma Combined Financial Information,” “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and “Index to Combined Financial Statements” of the Information Statement. Those sections are incorporated herein by reference.

The information required by this item is contained in the section “Change in Independent Registered Public Accounting Firm” of the Information Statement. That section is incorporated herein by reference.

(i) Financial Statements

The information required by this item is contained under the section “Index to Combined Financial Statements” beginning on page F-1 of the Information Statement. That section is incorporated herein by reference.

(ii) Exhibits

The following documents are filed as exhibits hereto:

SIGNATURES

Pursuant to the requirements of Section 12 of the Securities Exchange Act of 1934, the registrant has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized.

Dated: January 29, 2026