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

Rhea-AI Filing Summary

Y-mAbs Therapeutics completed a merger and associated tender offer resulting in cash-out of outstanding equity awards. On 09/16/2025 the purchaser completed a tender offer and merged with the issuer, making Y-mAbs an indirect wholly owned subsidiary of the buyer. Common shares were cancelled and converted into $8.60 per share in cash. The reporting person, a director, disposed of 5,825 shares and 25,080 restricted stock units were cashed out. All outstanding stock options and RSUs were cancelled and converted into cash pursuant to the merger terms, with options yielding cash equal to the excess of $8.60 over each option's exercise price; options with exercise prices at or above $8.60 were cancelled for no consideration.

Positive

• Merger completed and consideration of $8.60 per share was paid to holders
• All equity awards settled in cash pursuant to the Merger Agreement, providing liquidity to holders

Negative

• Reporting person no longer holds common stock following the reported dispositions and settlements
• Outstanding options were cancelled if their exercise price was equal to or above $8.60, receiving no consideration

Insights

Financial Analyst

TL;DR: Merger resulted in full cash-out of public equity and option/R.S.U. awards at $8.60 per share.

The Form 4 documents the mechanical settlement of equity holdings following the Merger Agreement dated August 4, 2025. The reporting director’s open common shares and RSUs were converted into cash at $8.60 per share; multiple option tranches were cashed out based on the spread to $8.60, while in-the-money and at-the-money outcomes are reflected by the option exercise-price comparisons listed. For investors, this confirms completion of the acquisition and elimination of public equity interests, removing public float and ending the company’s standalone equity valuation.

Corporate Governance Expert

TL;DR: Director-level holdings were settled per merger terms; equity incentives were uniformly converted to cash.

The filing shows governance-level alignment with the Merger Agreement: director-held RSUs and stock options were treated consistently with the deal terms, being cancelled and converted to cash consideration. The Form 4 clarifies that vested and unvested awards were both cashed out, and it references the Merger Agreement as controlling. This documents the cessation of the reporting person’s beneficial ownership post-closing and provides the contractual basis for award settlements.

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^*

GILL DAVID N

(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)

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

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)		D		5,825	D	$8.6(2)	0	D
Common Stock	09/16/2025(1)		D		25,080(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)	$11.16	09/16/2025(1)		D			24,000	(5)	04/24/2028	Common Stock	24,000	(5)	0	D
Employee Stock Option (right to buy)	$21.45	09/16/2025(1)		D			16,000	(5)	06/12/2029	Common Stock	16,000	(5)	0	D
Employee Stock Option (right to buy)	$48.67	09/16/2025(1)		D			11,000	(5)	06/23/2030	Common Stock	11,000	(5)	0	D
Employee Stock Option (right to buy)	$37.53	09/16/2025(1)		D			11,000	(5)	06/10/2031	Common Stock	11,000	(5)	0	D
Employee Stock Option (right to buy)	$16.64	09/16/2025(1)		D			16,000	(5)	07/15/2032	Common Stock	16,000	(5)	0	D
Employee Stock Option (right to buy)	$8.13	09/16/2025(1)		D			13,950	(5)	06/08/2033	Common Stock	13,950	(5)	0	D
Employee Stock Option (right to buy)	$12.01	09/16/2025(1)		D			14,545	(5)	06/11/2034	Common Stock	14,545	(5)	0	D
Employee Stock Option (right to buy)	$4.51	09/16/2025(1)		D			33,450	(5)	06/30/2035	Common Stock	33,450	(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.
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FAQ

What did Y-mAbs (YMAB) shareholders receive in the merger?

Shareholders received $8.60 per share in cash in exchange for each issued and outstanding common share as of the Effective Time.

How were RSUs and stock options handled in the Y-mAbs merger?

All RSUs and options were cancelled and converted into cash amounts: RSUs converted to $8.60 per underlying share; options converted to cash equal to (Merger Consideration minus exercise price) per share, with options priced >= $8.60 cancelled for no consideration.

Did the reporting director retain any Y-mAbs shares after the transaction?

No. The Form 4 shows the reporting person disposed of shares and had RSUs and options converted to cash, resulting in zero beneficial ownership reported following the transactions.

When was the tender offer and merger completed?

The transactions were completed on 09/16/2025, which is listed as the transaction and Effective Time for the conversions and cancellations.

How many options and RSUs were affected for the reporting person?

The reporting person had multiple option tranches totaling the listed amounts (for example, 24,000 options at $11.16, 33,450 at $4.51, and various other tranches) and 25,080 RSUs converted to cash.