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

Rhea-AI Filing Summary

Y-mAbs Therapeutics insider reported transactions tied to a completed merger. On September 16, 2025, pursuant to a Merger Agreement, a tender offer and subsequent merger resulted in Y-mAbs becoming an indirect wholly owned subsidiary of Perseus BidCo US, Inc. Common shares were cancelled and converted into cash consideration of $8.60 per share. Reporting person Joris Wilms surrendered 12,799 shares and 39,301 restricted stock units in exchange for the merger consideration, leaving 0 shares beneficially owned post-transaction.

Outstanding employee stock options were cancelled and converted into cash equal to the difference between the $8.60 Merger Consideration and each option's exercise price for in-the-money options; options with exercise prices at or above $8.60 were cancelled for no consideration. The Form 4 discloses the cash-out treatment for RSUs and options under the Merger Agreement.

Positive

• Merger completed, converting Y-mAbs into an indirect wholly owned subsidiary of Perseus BidCo US, Inc., which provides certainty of transaction outcome.
• Cash consideration of $8.60 per share was paid to shareholders and used to settle RSUs and in-the-money options, providing immediate cash realization for award holders.

Negative

• Reporting person holds 0 shares post-closing, indicating complete divestiture of direct equity position upon merger.
• Options with exercise prices equal to or above $8.60 were cancelled for no consideration, resulting in loss of value for holders of those awards.

Insights

M&A Specialist

TL;DR: Merger completed; equity awards cashed out at $8.60 per share, changing equity capital structure and eliminating public float.

The Form 4 documents a standard deal-closing mechanics: a tender offer followed by a merger that converted all public common shares into cash consideration of $8.60 per share. RSUs were settled for cash equal to the number of shares times $8.60 and in-the-money stock options were net-cashed for the spread. This eliminates remaining publicly traded shares and extinguishes outstanding equity awards per the Merger Agreement, which is material to shareholders and creditors because it effects a change from public company status to a privately held subsidiary.

Corporate Governance Expert

TL;DR: Insider holdings and incentive awards were cancelled/converted per merger terms, impacting executive compensation realizations.

The reporting shows the reporting person had both restricted stock units and multiple employee stock options converted into cash at closing. Several options with exercise prices above the $8.60 consideration were cancelled for no value, while vested and unvested awards were cashed out. This is a material governance event affecting equity-based compensation, vesting outcomes, and post-transaction incentives, and it confirms contractually prescribed treatment of awards in the merger documentation.

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^*

Wilms Joris

(Last) (First) (Middle)

C/O Y-MABS THERAPEUTICS, INC.

230 PARK AVENUE, SUITE 3350

(Street)

NEW YORK NY 10169

(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)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	SVP & CHIEF OPERATING OFFICER

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		12,799	D	$8.6(2)	0	D
Common Stock	09/16/2025(1)		D		39,301(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)	$4.38	09/16/2025(1)		D			20,000	(5)	08/22/2026	Common Stock	20,000	(5)	0	D
Employee Stock Option (right to buy)	$9.35	09/16/2025(1)		D			20,000	(5)	12/05/2027	Common Stock	20,000	(5)	0	D
Employee Stock Option (right to buy)	$21.97	09/16/2025(1)		D			20,000	(5)	12/11/2028	Common Stock	20,000	(5)	0	D
Employee Stock Option (right to buy)	$33.74	09/16/2025(1)		D			20,000	(5)	12/10/2029	Common Stock	20,000	(5)	0	D
Employee Stock Option (right to buy)	$53.88	09/16/2025(1)		D			20,000	(5)	12/15/2030	Common Stock	20,000	(5)	0	D
Employee Stock Option (right to buy)	$15.73	09/16/2025(1)		D			32,000	(5)	12/14/2031	Common Stock	32,000	(5)	0	D
Employee Stock Option (right to buy)	$9.51	09/16/2025(1)		D			20,000	(5)	04/26/2032	Common Stock	20,000	(5)	0	D
Employee Stock Option (right to buy)	$4.7	09/16/2025(1)		D			35,700	(5)	01/17/2033	Common Stock	35,700	(5)	0	D
Employee Stock Option (right to buy)	$4.55	09/16/2025(1)		D			32,000	(5)	01/26/2033	Common Stock	32,000	(5)	0	D
Employee Stock Option (right to buy)	$9.83	09/16/2025(1)		D			35,700	(5)	01/18/2034	Common Stock	35,700	(5)	0	D
Employee Stock Option (right to buy)	$6.16	09/16/2025(1)		D			42,900	(5)	01/17/2035	Common Stock	42,900	(5)	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.

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
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
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FAQ

What happened to Y-mAbs (YMAB) shares in the merger?

All issued and outstanding common shares were cancelled at the Effective Time and converted into $8.60 per share in cash under the Merger Agreement.

How were restricted stock units (RSUs) treated in the YMAB merger?

Each RSU was cancelled and converted into the right to receive cash equal to the number of shares issuable upon settlement multiplied by $8.60.

What happened to employee stock options after the YMAB merger?

Each outstanding option was cancelled and converted into the right to receive cash equal to the product of the number of shares subject to the option and the excess of $8.60 over the option's exercise price. Options with exercise prices ≥ $8.60 were cancelled for no consideration.

How many shares and RSUs did the reporting person surrender or have converted?

The Form 4 reports 12,799 shares surrendered and 39,301 RSUs converted into cash consideration, leaving 0 shares beneficially owned after the transaction.

When did the tender offer and merger close?

The tender offer and merger transactions were completed on September 16, 2025 according to the Form 4.