[Form 4] Y-mAbs Therapeutics, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Michael J. Rossi, President & CEO and Director of Y-mAbs Therapeutics (YMAB), reported disposition of his equity holdings in connection with a completed merger. Pursuant to a Merger Agreement dated August 4, 2025, a tender offer closed and the company merged into an indirect wholly owned subsidiary of the buyer on September 16, 2025. Each outstanding common share was cancelled for $8.60 per share in cash. The Form 4 shows reported disposals that reduced the reporting person’s direct common stock and derivative positions to zero following the Effective Time, including 7,982 shares and 129,101 RSU-related shares reflected as tendered or cancelled, multiple employee stock options (totaling 1,040,140 options across three series) converted into cash, and several RSU/PRSU awards likewise converted into cash under the Merger Agreement.

The footnotes explain that outstanding options were cashed out for the excess of the $8.60 merger consideration over their exercise prices (options with exercise prices at or above $8.60 were cancelled for no consideration), and that RSUs/PRSUs were converted into the right to receive cash equal to their underlying share count multiplied by $8.60.

Positive

• Completed merger providing a definite cash consideration of $8.60 per share
• All outstanding award settlements disclosed, including treatment of options, RSUs, and PRSUs under the Merger Agreement
• Reporting person’s transactions fully documented with footnotes tying outcomes to contractual terms

Negative

• Insider equity eliminated—the reporting person’s direct and derivative holdings reduced to zero, removing insider ownership alignment with public shareholders
• Options with exercise prices at or above $8.60 were cancelled for no consideration, representing a loss of potential upside for certain award holders

Insights

M&A Specialist

TL;DR: Insider equity positions were cashed out at $8.60 per share as part of a completed merger, eliminating remaining insider equity exposure.

The transaction reflects a typical deal consideration exchange where all outstanding common shares, options and RSU/PRSU awards were settled for cash under the Merger Agreement executed August 4, 2025, and effective September 16, 2025. The reporting person’s stock and derivative holdings were converted to cash: listed option pools (615,240; 214,200; 210,700) and RSU/PRSU grants (multiple tranches totaling tens of thousands of units) were treated consistent with standard merger mechanics—options converted to cash equal to the spread where in-the-money and otherwise cancelled; RSUs/PRSUs paid out based on underlying share counts times the $8.60 per-share cash consideration. This is a material corporate control event that fully monetized insider equity.

Corporate Governance Expert

TL;DR: CEO and director positions sold out through merger consideration, with all equity awards cancelled or cashed under contract terms.

From a governance perspective, the Form 4 documents that Michael J. Rossi’s direct and derivative ownership in YMAB was extinguished in connection with the merger. The filing discloses that RSUs, PRSUs and options were converted pursuant to the Merger Agreement into cash payments based on the $8.60 per-share consideration or cancelled if out-of-the-money, and that the reporting person held no remaining beneficial ownership post-closing. The filing properly attributes transactions to the merger mechanics and references the Merger Agreement for definitive terms.

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

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X

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person^*

Rossi Michael J

(Last) (First) (Middle)

C/O Y-MABS THERAPEUTICS, INC.

202 CARNEGIE CENTER, SUITE 301

(Street)

PRINCETON NJ 08540

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Y-mAbs Therapeutics, Inc. [ YMAB ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	PRESIDENT & CEO

3. Date of Earliest Transaction (Month/Day/Year)
09/16/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	09/16/2025(1)		U		7,982	D	$8.6(2)	0	D
Common Stock	09/16/2025(1)		D		129,101(3)	D	(4)	0	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Employee Stock Option (right to buy)	$5.75	09/16/2025(1)		D			615,240	(5)	11/06/2033	Common Stock	615,240	(5)	0	D
Employee Stock Option (right to buy)	$14.36	09/16/2025(1)		D			214,200	(5)	02/12/2034	Common Stock	214,200	(5)	0	D
Employee Stock Option (right to buy)	$6.16	09/16/2025(1)		D			210,700	(5)	01/17/2035	Common Stock	210,700	(5)	0	D
Restricted Stock Units(6)	(7)	09/16/2025(1)		D			18,000	(7)	(7)	Common Stock	18,000	(7)	0	D
Restricted Stock Units(6)	(7)	09/16/2025(1)		D			18,000	(7)	(7)	Common Stock	18,000	(7)	0	D
Restricted Stock Units(6)	(7)	09/16/2025(1)		D			18,000	(7)	(7)	Common Stock	18,000	(7)	0	D
Restricted Stock Units(6)	(7)	09/16/2025(1)		D			52,650	(7)	(7)	Common Stock	52,650	(7)	0	D
Restricted Stock Units(6)	(7)	09/16/2025(1)		D			52,650	(7)	(7)	Common Stock	52,650	(7)	0	D

Explanation of Responses:

1. Pursuant to the Agreement and Plan of Merger (the "Merger Agreement"), dated as of August 4, 2025, by and among Y-mAbs Therapeutics, Inc. (the "Issuer"), Yosemite Merger Sub, Inc. ("Purchaser"), Perseus BidCo US, Inc., a Delaware corporation ("Parent"), and Stark International Lux, a Luxembourg private limited liability company ("Ultimate Parent"), on September 16, 2025, Purchaser completed a tender offer for shares of common stock of the Issuer (each, a "Share") and thereafter merged with and into the Issuer, with the Issuer continuing as the surviving corporation and an indirect wholly owned subsidiary of Parent (the "Merger").

2. Pursuant to the terms of the Merger Agreement, the Shares were tendered at the Offer Acceptance Time (as defined in the Merger Agreement) in exchange for the right to receive $8.60 per Share, in cash, without interest, subject to any applicable withholding of taxes (the "Merger Consideration"). At the effective time of the Merger (being such date and at such time as the certificate of merger in respect of the Merger was duly filed with the Secretary of State of the State of Delaware in accordance with the DGCL) (the "Effective Time"), each issued and outstanding Share was cancelled in exchange for the Merger Consideration.

3. Represents restricted stock units ("RSUs") granted to the Reporting Person pursuant to the Issuer's 2018 Equity Incentive Plan. Each RSU represents a contingent right to receive one share of Common Stock on the vesting dates of the RSU.

4. At the Effective Time, pursuant to the Merger Agreement, each RSU award outstanding as of immediately prior to the Effective Time, whether vested or unvested, was cancelled and converted into the right to receive an amount in cash, without interest, equal to the product of (a) the total number of Shares issuable in settlement of such RSU award immediately prior to the Effective Time, multiplied by (b) the Merger Consideration.

5. At the Effective Time, pursuant to the Merger Agreement, each stock option ("Option") outstanding as of immediately prior to the Effective Time, whether vested or unvested, was cancelled and converted into the right to receive cash, without interest, equal to the product of (a) the total number of Shares subject to such Option immediately prior to the Effective Time, multiplied by (b) the excess of the Merger Consideration over the exercise price payable per Share under such Option. Any Options with an exercise price equal to or in excess of the Merger Consideration were cancelled for no consideration.

6. Performance-Based RSUs ("PRSUs") granted to the Reporting Person pursuant to the 2018 Equity Incentive Plan of Y-mAbs Therapeutics, Inc. Each PRSU represents a contingent right to receive one share of Common Stock on the vesting dates of the PRSU.

7. At the Effective Time, pursuant to the Merger Agreement, each PRSU award outstanding as of immediately prior to the Effective Time, whether vested or unvested, was cancelled and converted into the right to receive an amount in cash, without interest, equal to the product of (a) the maximum number of Shares issuable in settlement of such PRSU award immediately prior to the Effective Time, multiplied by (b) the Merger Consideration.

Remarks:

The foregoing descriptions in the footnotes to this Form 4 are qualified in their entirety by reference to the terms of the Merger Agreement. In the event of any conflict between the descriptions above and the terms set forth in the Merger Agreement, the terms set forth in the Merger Agreement shall control.

	/s/ John LaRocca, Attorney-in-Fact	09/18/2025
	** Signature of Reporting Person	Date
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FAQ

What did Michael J. Rossi report on Form 4 for YMAB?

The Form 4 reports that Michael J. Rossi, President & CEO and Director, had his common stock, stock options, RSUs and PRSUs converted or cancelled in connection with the merger, resulting in zero beneficial ownership following the Effective Time.

What cash consideration was paid per share in the YMAB merger?

The Merger Consideration was $8.60 per share in cash, without interest and subject to applicable tax withholding.

How were stock options treated in the merger?

Each outstanding option was cancelled and converted into the right to receive cash equal to the number of shares subject to the option multiplied by the excess of the $8.60 Merger Consideration over the option’s exercise price; options with exercise prices equal to or exceeding $8.60 were cancelled for no consideration.

How were RSUs and PRSUs handled at the Effective Time?

All RSU and PRSU awards, whether vested or unvested, were cancelled and converted into the right to receive cash equal to the number of shares issuable multiplied by $8.60 per share.

When did the merger and related transactions occur?

The tender offer and merger closed with an Effective Time on September 16, 2025, which is the transaction date reported on the Form 4.