EX-10.6



 Exhibit 10.6 

CYTOMX THERAPEUTICS, INC. 

EMPLOYEE STOCK PURCHASE PLAN 

1. Purpose. The purpose of this Plan is to provide Employees of the Company and Participating Subsidiaries with an opportunity
to purchase common stock of the Company through accumulated payroll deductions. It is the intention of the Company to have the Plan qualify as an “Employee Stock Purchase Plan” under Section 423 of the Code. The provisions of the
Plan, accordingly, shall be construed so as to extend and limit participation in a manner consistent with the requirements of that Section of the Code. 

2. Definitions. As used herein, the terms set forth below have the meanings assigned to them in this Section 2 and shall
include the plural as well as the singular. 
 “1933 Act” means the Securities Act of 1933, as amended. 

“1934 Act” means the Securities Exchange Act of 1934, as amended. 

“Board” means the Board of Directors of the Company. 

“Business Day” shall mean a day on which NASDAQ is open for trading. 

“Brokerage Account” means the account in which the Purchased Shares are held. 

“Code” means the Internal Revenue Code of 1986, as amended. 

“Committee” means the Compensation Committee of the Board, or the designee of the Compensation Committee. 

“Company” means CytomX Therapeutics, Inc., a Delaware corporation, or any successor thereto. 

“Compensation” means solely the base pay received by a Participant. Compensation does not include:
(1) commissions; (2) cash bonuses; (3) income related to stock option awards, stock grants and other equity incentive awards; (4) expense reimbursements; (5) relocation-related payments; (6) benefit plan payments
(including but not limited to short-term disability pay, long-term disability pay, maternity pay, military pay, tuition reimbursement and adoption assistance); (7) deceased pay; (8) income from non-cash and fringe benefits;
(9) severance payments; (10) overtime; or (11) other forms of compensation not specifically listed herein. 

“Employee” means any individual who is a common law employee of the Company or any other Participating Subsidiary. For
purposes of the Plan, the employment relationship shall be treated as continuing intact while the individual is on sick leave or other leave of absence approved by the Company or the Participating Subsidiary, as appropriate, and only to the extent
permitted under Section 423 of the Code. For purposes of the Plan, an individual who performs services for the Company or a Participating Subsidiary pursuant to an agreement (written or oral) that classifies such individual’s relationship
with the Company or a Participating Subsidiary as other than a common law employee shall not be considered an “employee” with respect to any period preceding the date on which a court or administrative agency issues a final determination
that such individual is an “employee.” 







 “Enrollment Date” means the first Business Day of each Offering Period.

 “Exercise Date” means the last Business Day of each Offering Period. 

“Fair Market Value” on or as of any date means the “NASDAQ Official Closing Price” (as defined on
www.nasdaq.com) (or such substantially similar successor price thereto) for a Share as reported on www.nasdaq.com (or a substantially similar successor website) on the relevant valuation date or, if no NASDAQ Official Closing Price is reported on
such date, on the preceding day on which a NASDAQ Official Closing Price was reported; or, if the Shares are no longer listed on NASDAQ, the closing price for Shares as reported on the official website for such other exchange on which the Shares are
listed. 
 “NASDAQ” means the Nasdaq Global Market. 

“Offering Period” means every six-month period beginning each January 1st, and July 1st or such other period
designated by the Committee; provided that in no event shall an Offering Period exceed twenty-seven (27) months. The first Offering Period under the Plan shall commence on July 1, 2016. 

“Option” means an option granted under this Plan that entitles a Participant to purchase Shares. 

“Participant” means an Employee who satisfies the requirements of Sections 3 and 5 of the Plan. 

“Participating Subsidiary” means each Subsidiary other than those that the Committee or the Board has excluded from
participation in the Plan. 
 “Plan” means this CytomX Therapeutics, Inc. Employee Stock Purchase Plan. 

“Purchase Account” means the account used to purchase Shares through the exercise of Options under the Plan. 

“Purchase Price” shall be eighty-five percent (85%) of the lesser of (i) the Fair Market Value of a Share on
the applicable Enrollment Date, or (ii) the Fair Market Value of a Share on the Exercise Date for such Offering Period; provided, however, that the Committee may determine a different per share Purchase Price provided that such per share
Purchase Price is communicated to Participants prior to the beginning of the Offering Period and provided that in no event shall such per share Purchase Price be less than the lesser of 85% of (i) the Fair Market Value of a Share on the
applicable Enrollment Date or (ii) the Fair Market Value of a Share on the Exercise Date. 
 “Purchased Shares”
means the full Shares issued or delivered pursuant to the exercise of Options under the Plan. 

  
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 “Shares” means the common stock, par value $0.00001 per share, of the
Company. 
 “Subsidiary” means an entity, domestic or foreign, of which not less than 50% of the voting equity is
held by the Company or a Subsidiary, whether or not such entity now exists or is hereafter organized or acquired by the Company or a Subsidiary; provided such entity is also a “subsidiary” within the meaning of Section 424 of the
Code. 
 “Termination Date” means the date on which a Participant terminates employment or on which the Participant
ceases to provide services to the Company or a Subsidiary as an employee, and specifically does not include any period following that date which the Participant may be eligible for or in receipt of other payments from the Company including in lieu
of notice or termination or severance pay or as wrongful dismissal damages. 
 3. Eligibility. 

(a) Only Employees of the Company or a Participating Subsidiary shall be eligible to be granted Options under the Plan and, in no event may a
Participant be granted an Option under the Plan following his or her Termination Date. 
 (b) Any provisions of the Plan to the contrary
notwithstanding, no Employee shall be granted an Option under the Plan if (i) immediately after the grant, such Employee (or any other person whose stock would be attributed to such Employee pursuant to Section 424(d) of the Code) would
own capital stock of the Company and/or hold outstanding Options or options to purchase stock possessing five percent (5%) or more of the total combined voting power or value of all classes of stock of the Company or of any of its Subsidiaries,
or (ii) such Option would permit his or her rights to purchase stock under all employee stock purchase plans (described in Section 423 of the Code) of the Company and its Subsidiaries to accrue at a rate that exceeds twenty-five thousand
dollars ($25,000) of the Fair Market Value of such stock (determined at the time each such Option is granted) for each calendar year in which such Option is outstanding at any time. No Participant may purchase more than 6,000 Shares during any
Offering Period. 
 4. Exercise of an Option. Options shall be exercised on behalf of Participants in the Plan every Exercise
Date, using payroll deductions that have accumulated in the Participants’ Purchase Accounts during the immediately preceding Offering Period or that have been retained from a prior Offering Period pursuant to Section 8 hereof. 

5. Participation. 

(a) An Employee shall be eligible to participate on the first Enrollment Date that occurs at least 90 days after such Employee’s first
date of employment with the Company or a Participating Subsidiary; provided, that such Employee properly completes and submits an election form by the deadline prescribed by the Company. 

(b) An Employee who does not become a Participant on the first Enrollment Date on which he or she is eligible may thereafter become a
Participant on any subsequent Enrollment Date by properly completing and submitting an election form by the deadline prescribed by the Company. 

  
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 (c) Payroll deductions for a Participant shall commence on the first payroll date following the
Enrollment Date and shall end on the last payroll date in the Offering Period to which such authorization is applicable, unless sooner terminated by the Participant as provided in Section 12 hereof. 

6. Payroll Deductions. 

(a) A Participant shall elect to have payroll deductions made during an Offering Period equal to no less than 1% of the Participant’s
Compensation up to a maximum of 15% (or such greater amount as the Committee establishes from time to time). The amount of such payroll deductions shall be in whole percentages (for example, 3%, 12%, 15%). All payroll deductions made by a
Participant shall be credited to his or her Purchase Account. A Participant may not make any additional payments into his or her Purchase Account. 

(b) A Participant may not increase or decrease the rate of payroll deductions during an Offering Period. A Participant may change his or her
payroll deduction percentage under subsection (a) above for any subsequent Offering Period by properly completing and submitting an election change form in accordance with the procedures prescribed by the Committee. The change in amount shall
be effective as of the first Enrollment Date following the date of filing of the election change form. 
 (c) Notwithstanding the foregoing,
to the extent necessary to comply with Section 423(b)(8) of the Code and Section 3(b) hereof, a Participant’s payroll deductions may be decreased to zero percent (0%) at any time during an Offering Period. Payroll deductions shall
recommence at the rate provided in such Participant’s election form at the beginning of the first Offering Period which is scheduled to end in the following calendar year, unless terminated by the Participant as provided in Section 12
hereof. 
 7. Grant of Option. On the applicable Enrollment Date, each Participant in an Offering Period shall be granted an
Option to purchase on the next following Exercise Date a number of full Shares determined by dividing such Participant’s payroll deductions accumulated prior to such Exercise Date and retained in the Participant’s Purchase Account as of
the Exercise Date by the applicable Purchase Price. 
 8. Exercise of Option. A Participant’s Option for the purchase of
Shares shall be exercised automatically on the Exercise Date, and the maximum number of Shares subject to the Option shall be purchased for such Participant at the applicable Purchase Price with the accumulated payroll deductions in his or her
Purchase Account. No fractional Shares shall be purchased; any payroll deductions accumulated in a Participant’s Purchase Account which are not sufficient to purchase a full Share shall be retained in the Purchase Account for the next
subsequent Offering Period, subject to earlier withdrawal by the Participant as provided in Section 12 hereof. All other payroll deductions accumulated in a Participant’s Purchase Account and not used to purchase Shares on an Exercise Date
shall be distributed to the Participant. During a Participant’s lifetime, a Participant’s Option is exercisable only by him or her. The Company shall satisfy the exercise of all Participants’ Options for the purchase of Shares through
(a) the issuance of authorized but unissued Shares, (b) the transfer of treasury Shares, (c) the purchase of Shares on behalf of the applicable Participants on the open market through an independent broker and/or (d) a
combination of the foregoing. 

  
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 9. Issuance of Stock. The Shares purchased by each Participant shall be issued in
book entry form and shall be considered to be issued and outstanding to such Participant’s credit as of the end of the last day of each Offering Period. The Committee may permit or require that shares be deposited directly in a Brokerage
Account with one or more brokers designated by the Committee or to one or more designated agents of the Company, and the Committee may use electronic or automated methods of share transfer. The Committee may require that Shares be retained with such
brokers or agents for a designated period of time and/or may establish other procedures to permit tracking of disqualifying dispositions of such Shares, and may also impose a transaction fee with respect to a sale of Shares issued to a
Participant’s credit and held by such a broker or agent. The Committee may permit Shares purchased under the Plan to participate in a dividend reinvestment plan or program maintained by the Company, and establish a default method for the
payment of dividends. 
 10. Approval by Stockholders. Notwithstanding the above, the Plan is expressly made subject to the
approval of the stockholders of the Company within 12 months before or after the date the Plan is adopted by the Board. Such stockholder approval shall be obtained in the manner and to the degree required under applicable federal and state law. If
the Plan is not so approved by the stockholders within 12 months before or after the date the Plan is adopted by the Board, this Plan shall not come into effect. 

11. Administration. 

(a) Powers and Duties of the Committee. The Plan shall be administered by the Committee. Subject to the provisions of the Plan,
Section 423 of the Code and the regulations thereunder, the Committee shall have the discretionary authority to determine the time and frequency of granting Options, the terms and conditions of the Options and the number of Shares subject to
each Option. The Committee shall also have the discretionary authority to do everything necessary and appropriate to administer the Plan, including, without limitation, interpreting the provisions of the Plan (but any such interpretation shall not
be inconsistent with the provisions of Section 423 of the Code). All actions, decisions and determinations of, and interpretations by the Committee with respect to the Plan shall be final and binding upon all Participants and upon their
executors, administrators, personal representatives, heirs and legatees. No member of the Board or the Committee shall be liable for any action, decision, determination or interpretation made in good faith with respect to the Plan or any Option
granted hereunder. The Plan shall be administered so as to ensure that all Participants have the same rights and privileges as are provided by Section 423(b)(5) of the Code. 

(b) Administrator. The Company, Board or the Committee may engage the services of a brokerage firm or financial institution (the
“Administrator”) to perform certain ministerial and procedural duties under the Plan including, but not limited to, mailing and receiving notices contemplated under the Plan, determining the number of Purchased Shares for each
Participant, maintaining or causing to be maintained the Purchase Account and the Brokerage Account, disbursing funds maintained in the Purchase Account or proceeds from the sale of Shares through the Brokerage Account, and filing with the
appropriate tax authorities proper tax returns and forms (including information returns) and providing to each Participant statements as required by law or regulation. 

  
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 (c) Indemnification. Each person who is or shall have been (a) a member of the Board,
(b) a member of the Committee, or (c) an officer or employee of the Company to whom authority was delegated in relation to this Plan, shall be indemnified and held harmless by the Company against and from any loss, cost, liability or
expense that may be imposed upon or reasonably incurred by him or her in connection with or resulting from any claim, action, suit or proceeding to which he or she may be a party or in which he or she may be involved by reason of any action taken or
failure to act under the Plan and against and from any and all amounts paid by him or her in settlement thereof, with the Company’s approval, or paid by him or her in satisfaction of any judgment in any such claim, action, suit or proceeding
against him or her; provided, however, that he or she shall give the Company an opportunity, at its own expense, to handle and defend the same before he or she undertakes to handle and defend it on his or her own behalf, unless such loss, cost,
liability or expense is a result of his or her own willful misconduct or except as expressly provided by statute. 
 The foregoing right of indemnification
shall not be exclusive of any other rights of indemnification to which such persons may be entitled under the Company’s certificate of incorporation or bylaws, any contract with the Company, as a matter of law, or otherwise, or of any power
that the Company may have to indemnify them or hold them harmless. 
 12. Withdrawal. A Participant may withdraw from the Plan
by properly completing and submitting to the Company a withdrawal form in accordance with the procedures prescribed by the Committee, which must be submitted prior to the date specified by the Committee before the last day of the applicable Offering
Period. Upon withdrawal, any payroll deductions credited to the Participant’s Purchase Account prior to the effective date of the Participant’s withdrawal from the Plan will be returned to the Participant. No further payroll deductions for
the purchase of Shares will be made during subsequent Offering Periods, unless the Participant properly completes and submits an election form, by the deadline prescribed by the Company. A Participant’s withdrawal from an offering will not have
any effect upon his or her eligibility to participate in the Plan or in any similar plan that may hereafter be adopted by the Company. 

13. Termination of Employment. On the Termination Date of a Participant for any reason prior to the applicable Exercise Date,
whether voluntary or involuntary, and including termination of employment due to retirement, death or as a result of liquidation, dissolution, sale, merger or a similar event affecting the Company or a Participating Subsidiary, the corresponding
payroll deductions credited to his or her Purchase Account will be returned to him or her or, in the case of the Participant’s death, to the person or persons entitled thereto under Section 16, and his or her Option will be automatically
terminated. 
 14. Interest. No interest shall accrue on the payroll deductions of a Participant in the Plan. 

15. Stock. 

  
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 (a) The stock subject to Options shall be common stock of the Company as traded on the NASDAQ or
on such other exchange as the Shares may be listed. 
 (b) Subject to adjustment upon changes in capitalization of the Company as provided
in Section 18 hereof, the maximum aggregate number of Shares which shall be made available under the Plan shall be 354,466 Shares, plus an annual increase to be added on the first day of each calendar year beginning with 2016, equal to the
lesser of (i) 675,000 Shares, (ii) one percent (1%) of the then-outstanding Shares on such date, or (iii) an amount determined by the Committee. If, on a given Exercise Date, the number of Shares with respect to which Options are
to be exercised exceeds the number of Shares then available under the Plan, the Committee shall make a pro rata allocation of the Shares remaining available for purchase in as uniform a manner as shall be practicable and as it shall determine to be
equitable. 
 (c) A Participant shall have no interest or voting right in Shares covered by his or her Option until such Option has been
exercised and the Participant has become a holder of record of Shares acquired pursuant to such exercise. 
 16. Designation of
Beneficiary. The Committee may permit Participants to designate beneficiaries to receive any Purchased Shares or payroll deductions, if any, in the Participant’s accounts under the Plan in the event of such Participant’s death.
Beneficiary designations shall be made in accordance with procedures prescribed by the Committee. If no properly designated beneficiary survives the Participant, the Purchased Shares and payroll deductions, if any, will be distributed to the
Participant’s estate. 
 17. Assignability of Options. Neither payroll deductions credited to a Participant’s
Purchase Account nor any rights with regard to the exercise of an Option or to receive Shares under the Plan may be assigned, transferred, pledged or otherwise disposed of in any way (other than by will, the laws of descent and distribution or as
provided in Section 16 hereof) by the Participant. Any such attempt at assignment, transfer, pledge or other disposition shall be without effect, except that the Company may treat such act as an election to withdraw from an Offering Period in
accordance with Section 12 hereof. 
 18. Adjustment of Number of Shares Subject to Options. 

(a) Adjustment. Subject to any required action by the stockholders of the Company, the maximum number of securities available for
purchase under the Plan, as well as the price per security and the number of securities covered by each Option under the Plan which has not yet been exercised shall be appropriately adjusted in the event of any stock split, reverse stock split,
stock dividend, combination or reclassification of the common stock of the Company, or any other increase or decrease in the number of Shares effected without receipt of consideration by the Company; provided, however, that conversion of any
convertible securities of the Company shall not be deemed to have been “effected without receipt of consideration.” Such adjustment shall be made by the Board or the Committee, whose determination in that respect shall be final, binding
and conclusive. If any such adjustment would result in a fractional security being available under the Plan, such fractional security shall be disregarded. Except as expressly provided herein, no issuance by the Company of shares of stock of any
class, or securities convertible into shares of stock of any class, shall affect, and no adjustment by reason thereof 

  
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shall be made with respect to, the number or price of Shares subject to an Option. The Options granted pursuant to the Plan shall not be adjusted in a manner that causes the Options to fail to
qualify as options issued pursuant to an “employee stock purchase plan” within the meaning of Section 423 of the Code. 
 (b)
Dissolution or Liquidation. In the event of the proposed dissolution or liquidation of the Company, the Offering Period then in progress will terminate immediately prior to the consummation of such proposed action, unless otherwise provided
by the Board, and the Board may either provide for the purchase of Shares as of the date on which such Offering Period terminates or return to each Participant the payroll deductions credited to such Participant’s Purchase Account. 

(c) Merger or Asset Sale. In the event of a proposed sale of all or substantially all of the assets of the Company, or the merger of
the Company with or into another corporation, each outstanding Option shall be assumed or an equivalent option substituted by the successor corporation or a parent or subsidiary of the successor corporation, unless the Board determines, in the
exercise of its sole discretion, that in lieu of such assumption or substitution to either terminate all outstanding Options and return to each Participant the payroll deductions credited to such Participant’s Purchase Account or to provide for
the Offering Period in progress to end on a date prior to the consummation of such sale or merger. 
 19. Amendments or Termination of
the Plan. 
 (a) The Board or the Committee may at any time and for any reason amend, modify, suspend, discontinue or terminate the
Plan without notice; provided that no Participant’s existing rights in respect of existing Options are adversely affected thereby. To the extent necessary to comply with Section 423 of the Code (or any other applicable law, regulation or
stock exchange rule), the Company shall obtain stockholder approval in such a manner and to such a degree as required. 
 (b) Without
stockholder consent and without regard to whether any Participant rights may be considered to have been “adversely affected,” the Board or the Committee shall be entitled to change the Purchase Price, Offering Periods, limit or increase
the frequency and/or number of changes in the amount withheld during an Offering Period, establish the exchange ratio applicable to amounts withheld in a currency other than U.S. dollars, permit payroll withholding in an amount less than or greater
than the amount designated by a Participant in order to adjust for delays or mistakes in the Company’s processing of properly completed withholding elections, establish reasonable waiting and adjustment periods and/or accounting and crediting
procedures to ensure that amounts applied toward the purchase of Shares for each Participant properly correspond with amounts withheld from the Participant’s Compensation, and establish such other limitations or procedures as the Board or the
Committee determines in its sole discretion advisable which are consistent with the Plan; provided, however, that changes to (i) the Purchase Price, (ii) the Offering Period, (iii) the maximum percentage of Compensation that may be
deducted pursuant to Section 6(a) or (iv) the maximum number of Shares that may be purchased in an Offering Period, shall not be effective until communicated to Participants in a reasonable manner, with the determination of such reasonable
manner in the sole discretion of the Board or the Committee. 

  
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 20. No Other Obligations. The receipt of an Option pursuant to the Plan shall
impose no obligation upon the Participant to purchase any Shares covered by such Option. Nor shall the granting of an Option pursuant to the Plan constitute an agreement or an understanding, express or implied, on the part of the Company to employ
the Participant for any specified period. 
 21. Notices and Communication. Any notice or other form of communication which
the Company or a Participant may be required or permitted to give to the other shall be provided through such means as designated by the Committee, including but not limited to any paper or electronic method. 

22. Condition Upon Issuance of Shares. 

(a) Shares shall not be issued with respect to an Option unless the exercise of such Option and the issuance and delivery of such Shares
pursuant thereto shall comply with all applicable provisions of law, domestic or foreign, including, without limitation, the 1933 Act and the 1934 Act and the rules and regulations promulgated thereunder, and the requirements of any stock exchange
upon which the Shares may then be listed, and shall be further subject to the approval of counsel for the Company with respect to such compliance. 

(b) As a condition to the exercise of an Option, the Company may require the person exercising such Option to represent and warrant at the
time of any such exercise that the Shares are being purchased only for investment and without any present intention to sell or distribute such Shares if, in the opinion of counsel for the Company, such a representation is required by any of the
aforementioned applicable provisions of law. 
 23. General Compliance. The Plan will be administered and Options will be
exercised in compliance with the 1933 Act, the 1934 Act and all other applicable securities laws and Company policies, including without limitation, any insider trading policy of the Company. 

24. Term of the Plan. The Plan shall become effective upon the earlier to occur of its adoption by the Board or its approval by
the stockholders of the Company and shall continue in effect for a term of ten (10) years, unless earlier terminated pursuant to Section 19. 

25. Governing Law. The Plan and all Options granted hereunder shall be construed in accordance with and governed by the laws of
the State of Delaware without reference to choice of law principles and subject in all cases to the Code and the regulations thereunder. 

26. Non-U.S. Participants. To the extent permitted under Section 423 of the Code, without the amendment of the Plan, the
Company may provide for the participation in the Plan by Employees who are subject to the laws of foreign countries or jurisdictions on such terms and conditions different from those specified in the Plan as may in the judgment of the Company be
necessary or desirable to foster and promote achievement of the purposes of the Plan and, in furtherance of such purposes the Company may make such modifications, amendments, procedures, subplans and the like as may be necessary or advisable to
comply with provisions of laws of other countries or jurisdictions in which the Company or the Participating Subsidiaries operate or have employees. Each subplan shall constitute a separate “offering” under this Plan in accordance with
Treas. Reg. §1.423-2(a). 

  
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