CytomX Therapeutics (CTMX) CEO sells shares to cover RSU tax obligations

Rhea-AI Filing Summary

CytomX Therapeutics CEO Sean A. McCarthy reported a tax-driven share sale. He sold 118,969 shares of common stock on March 17, 2026 at an average price of $6.423 per share, solely to satisfy tax and other government withholding obligations linked to vesting restricted stock units.

After this transaction, he directly holds 1,078,922 common shares, which include 457,500 RSUs, and indirectly holds 93,158 shares through the Sean A. McCarthy 2018 Trust, where he serves as trustee. The filing shows no remaining derivative securities such as stock options or warrants.

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

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

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

X

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

McCarthy Sean A.

(Last) (First) (Middle)

C/O CYTOMX THERAPEUTICS, INC.

151 OYSTER POINT BLVD., STE. 400

(Street)

SOUTH SAN FRANCISCO CALIFORNIA 94080

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
CytomX Therapeutics, Inc. [ CTMX ]

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

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

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
03/17/2026

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

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

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

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	03/17/2026		S(1)		118,969	D	$6.423	1,078,922(2)	D
Common Stock								93,158	I	See footnote(3)

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

Explanation of Responses:

1. The shares were sold solely to satisfy tax or other government withholding obligations in connection with the vesting of restricted stock units ("RSUs").

2. Includes 457,500 RSUs.

3. Shares held by Sean A. McCarthy 2018 Trust, of which Reporting Person is trustee.

	/s/ Lloyd Rowland, as Attorney-in-Fact for Sean A. McCarthy	03/19/2026
	** 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).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)

FAQ

What insider transaction did CytomX (CTMX) report for CEO Sean McCarthy?

CytomX reported that CEO Sean A. McCarthy sold 118,969 common shares on March 17, 2026 at an average price of $6.423. The shares were sold solely to cover tax and government withholding obligations from vesting restricted stock units, not as a discretionary open-market sale.

Why did CytomX (CTMX) CEO Sean McCarthy sell 118,969 shares?

The sale of 118,969 CytomX shares by CEO Sean McCarthy was done solely to satisfy tax and other government withholding obligations arising from the vesting of restricted stock units. This type of transaction is typically mechanical and related to compensation, rather than a change in his investment view.

How many CytomX (CTMX) shares does CEO Sean McCarthy hold after the transaction?

Following the March 17, 2026 transaction, Sean McCarthy directly holds 1,078,922 CytomX common shares, including 457,500 restricted stock units. He also indirectly holds 93,158 additional shares through the Sean A. McCarthy 2018 Trust, where he serves as trustee and has authority over those shares.

Was the CytomX (CTMX) CEO’s share sale linked to options or other derivatives?

The reported transaction was tied to the vesting of restricted stock units, not to stock options or other derivatives. The filing’s derivative section shows no remaining derivative positions, indicating the event related to equity awards that had already converted into common shares at vesting.

Is the CytomX (CTMX) CEO’s share sale a routine tax-withholding event?

Yes. The footnote states the shares were sold solely to satisfy tax or other government withholding obligations from RSU vesting. Such sales are typically routine, compensation-related events meant to cover required taxes, rather than voluntary portfolio rebalancing or a directional bet on the stock.

How are the indirectly held CytomX (CTMX) shares owned by Sean McCarthy structured?

The filing states that 93,158 CytomX shares are held by the Sean A. McCarthy 2018 Trust. Sean McCarthy is the trustee of this trust, which means he has authority over those shares, and they are reported as his indirect beneficial ownership in addition to his direct holdings.