UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): April 4, 2025

PULMATRIX, INC.

(Exact name of registrant as specified in its charter)

945 Concord Street, Suite 1217

Framingham, MA 01701

(Address of principal executive offices) (Zip Code)

(888) 355-4440

(Registrant’s telephone number, including area code)

N/A

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

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

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

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. ☐

(a) Resignation of Independent Registered Public Accounting Firm

On April 4, 2025, Pulmatrix, Inc. (the “Company”) was notified by Marcum LLP (“Marcum”) that Marcum resigned as the independent registered accounting firm of the Company. On November 1, 2024, CBIZ CPAs P.C. (“CBIZ”) acquired the attest business of Marcum. Substantially all of the partners and staff that provided attestation services with Marcum joined CBIZ CPAs P.C. On April 4, 2025, Marcum resigned as auditors of the Company and with the approval of the Audit Committee of the Company’s Board of Directors, CBIZ was engaged as the Company’s independent registered public accounting firm.

The reports of Marcum on the Company’s consolidated financial statements for the years ended December 31, 2024, and December 31, 2023, did not contain an adverse opinion or a disclaimer of opinion, and was not qualified or modified as to uncertainty, audit scope, or accounting principles.

During the two most recent fiscal years ended December 31, 2024, and December 31, 2023, and the subsequent interim period through April 4, 2025, there were no disagreements (as defined in Item 304(a)(1)(iv) of Regulation S-K of the Securities Exchange Act of 1934, as amended (“Regulation S-K”) and the related instructions to Item 304 of Regulation S-K) with Marcum on any matter of accounting principles or practices, financial statement disclosure, or auditing scope or procedure, which disagreements, if not resolved to the satisfaction of Marcum, would have caused Marcum to make reference to the subject matter of the disagreements in connection with its reports on the Company’s consolidated financial statements for such years. Also during this time, there were no “reportable events,” as defined in Item 304(a)(1)(v) of Regulation S-K.

The Company provided Marcum with a copy of the above disclosures and requested that Marcum furnish the Company with a letter addressed to the Securities and Exchange Commission stating whether or not it agrees with the statements made above. A copy of Marcum’s letter dated April 8, 2025, is attached as Exhibit 16.1 to this Current Report on Form 8-K.

(b) Engagement of New Independent Registered Public Accounting Firm

On April 4, 2025, the Audit Committee engaged CBIZ as the Company’s independent registered public accounting firm for the fiscal year ended December 31, 2025. In connection with the engagement, CBIZ will prepare the report on the Company’s consolidated financial statements for the year ending December 31, 2025. During the fiscal years ended December 31, 2024, and December 31, 2023, and the subsequent interim period through April 4, 2025, neither the Company nor anyone on its behalf has consulted with CBIZ regarding (i) the application of accounting principles to any specified transaction, either completed or proposed or the type of audit opinion that might be rendered on the Company’s consolidated financial statements, and neither a written report nor oral advice was provided to the Company that CBIZ concluded was an important factor considered by the Company in reaching a decision as to any accounting, auditing, or financial reporting issue, or (ii) any matter that was either the subject of a “disagreement,” as defined in Item 304(a)(1)(iv) of Regulation S-K, or a “reportable event,” as defined in Item 304(a)(1)(v) of Regulation S-K.

(d) Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.