Michael J. Rossi - 16 Sep 2025 Form 4 Insider Report for Y-mAbs Therapeutics, Inc. (YMAB)

Reporting relationship: PRESIDENT & CEO, Director
Issuer ticker: YMAB
Reported as of: 16 Sep 2025
Net transaction value: -$68,645
SEC form: 4
Accepted by SEC: 18 Sep 2025, 21:08:14 UTC
Prior SEC filing: 11 Mar 2025
Source filing: View source filing
Reporting owner signature: /s/ John LaRocca, Attorney-in-Fact

Key filing fact

Michael J. Rossi filed Form 4 for Y-mAbs Therapeutics, Inc. (YMAB) on 18 Sep 2025.

Key facts

This page summarizes Michael J. Rossi's Form 4 filing for Y-mAbs Therapeutics, Inc. (YMAB).
10 reported transactions and 8 derivative rows are listed below.
Accepted by SEC: 18 Sep 2025, 21:08.

Change

Previous filing in this sequence was filed on 11 Mar 2025.
Current net transaction value: -$68,645.

Research use

This tells you what this filing adds before you inspect full transaction and derivative tables.
You can trace every row back to the original SEC filing document.

Evidence

Filed on Form 4

Ownership activity is grounded in SEC Form 4 disclosures.

View source filing

Reporting Owners (1)

CIK 0001948795 Primary reporting owner

Rossi Michael J

Relationship: PRESIDENT & CEO, Director
Address: C/O Y-MABS THERAPEUTICS, INC., 202 CARNEGIE CENTER, SUITE 301, PRINCETON
Signature: /s/ John LaRocca, Attorney-in-Fact
Signature date: 18 Sep 2025

Reported non-derivative transactions

Shares, units, or other non-derivative securities reported in this filing.

YMAB transaction

Common Stock

Disposition pursuant to a tender of shares in a change of control transaction

Transaction value: $68,645
Shares: -7,982
Change %: -100%
Price: $8.60
Shares after: 0
Date: 16 Sep 2025
Ownership: Direct
Footnotes: F1, F2

YMAB transaction

Common Stock

Disposed to Issuer

Transaction value
Shares: -129,101
Change %: -100%
Price
Shares after: 0
Date: 16 Sep 2025
Ownership: Direct
Footnotes: F1, F3, F4

Reported derivative securities

Options, warrants, convertible securities, or similar derivative positions disclosed in the filing.

YMAB transaction Derivative

Employee Stock Option (right to buy)

Disposed to Issuer

Transaction value
Shares: -615,240
Change %: -100%
Price
Shares after: 0
Date: 16 Sep 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 615,240
Exercise price: $5.75
Footnotes: F1, F5

YMAB transaction Derivative

Employee Stock Option (right to buy)

Disposed to Issuer

Transaction value
Shares: -214,200
Change %: -100%
Price
Shares after: 0
Date: 16 Sep 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 214,200
Exercise price: $14.36
Footnotes: F1, F5

YMAB transaction Derivative

Employee Stock Option (right to buy)

Disposed to Issuer

Transaction value
Shares: -210,700
Change %: -100%
Price
Shares after: 0
Date: 16 Sep 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 210,700
Exercise price: $6.16
Footnotes: F1, F5

YMAB transaction Derivative

Restricted Stock Units

Disposed to Issuer

Transaction value
Shares: -18,000
Change %: -100%
Price
Shares after: 0
Date: 16 Sep 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 18,000
Exercise price
Footnotes: F1, F6, F7

YMAB transaction Derivative

Restricted Stock Units

Disposed to Issuer

Transaction value
Shares: -18,000
Change %: -100%
Price
Shares after: 0
Date: 16 Sep 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 18,000
Exercise price
Footnotes: F1, F6, F7

YMAB transaction Derivative

Restricted Stock Units

Disposed to Issuer

Transaction value
Shares: -18,000
Change %: -100%
Price
Shares after: 0
Date: 16 Sep 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 18,000
Exercise price
Footnotes: F1, F6, F7

YMAB transaction Derivative

Restricted Stock Units

Disposed to Issuer

Transaction value
Shares: -52,650
Change %: -100%
Price
Shares after: 0
Date: 16 Sep 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 52,650
Exercise price
Footnotes: F1, F6, F7

YMAB transaction Derivative

Restricted Stock Units

Disposed to Issuer

Transaction value
Shares: -52,650
Change %: -100%
Price
Shares after: 0
Date: 16 Sep 2025
Ownership: Direct
Underlying class: Common Stock
Underlying amount: 52,650
Exercise price
Footnotes: F1, F6, F7

^* marks a reported price that did not pass the local price check.

Additional SEC filing notes

Filing notes and footnotes

Section 16 status

Michael J. Rossi is no longer subject to Section 16 filing requirements. Form 4 or Form 5 obligations may still apply in specific circumstances.

Explanation of responses 7 footnotes

Footnote F1

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").

Footnote F2

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.

Footnote F3

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.

Footnote F4

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.

Footnote F5

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.

Footnote F6

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.

Footnote F7

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.

SEC 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.