Exhibit 10.43

May 29, 2015

Bayer Healthcare LLC
100 Bayer Boulevard
PO Box 915
Whippany, NJ 07981
Attention: Sr. VP and General Counsel
Facsimile: XXXXXXXXXX

Re:    Side Letter Regarding Collaboration Agreement

Dear Sir or Madam:

Reference is hereby made to the Collaboration Agreement, dated April 22, 1994,
as amended on April 24, 1996 (the “First Amendment”), on February 1, 1999 (the
“Second Amendment”), on March 6, 2006 pursuant to the U.S. Co-Promotion
Agreement (the “Co-Promotion Agreement”) and on October 11, 2011 (the “Fourth
Amendment”) (such agreement as amended by the First Amendment, Second Amendment,
Co-Promotion Agreement and Fourth Amendment being referred to herein as the
“Collaboration Agreement”) by and between Onyx Pharmaceuticals, Inc., a Delaware
corporation having its principal place of business in South San Francisco,
California (“Onyx”), and Bayer HealthCare LLC, a Delaware company having its
principal place of business in Whippany, New Jersey and the
successor-in-interest to Bayer Corporation (“Bayer” and, together with Onyx, the
“Parties”). Capitalized terms used but not otherwise defined in this letter
shall have the meanings assigned to such terms in the Collaboration Agreement.
In order to operationalize the collaboration more efficiently, the Parties
desire to modify certain terms of the Collaboration Agreement as set forth in
this letter.
In consideration of the foregoing and for other good and valuable consideration,
the receipt and sufficiency of which is hereby acknowledged, the Parties hereby
agree as follows:
1.Co-Promotion Agreement. The Parties hereby acknowledge and agree that the
Co-Promotion Agreement shall be terminated, effective as of June 30, 2015 (the
“Termination Date”), and, except as set forth in Section 10.6 of the
Co-Promotion Agreement or as otherwise expressly set forth herein, the
provisions of the Co-Promotion Agreement shall have no further force or effect
from and after the Termination Date.
a.
The Parties hereby agree that, notwithstanding anything to the contrary in the
Collaboration Agreement, during the U.S. Royalty Term (as defined below), Bayer
shall have exclusive authority and control over the commercialization of the
Collaboration Products in the United States (including control over when and how
to discontinue commercialization of the Collaboration Products in the United
States, provided, however, that, if Bayer elects to discontinue
commercialization of the Collaboration Products in the United States, Onyx shall
have the right to assume exclusive authority and control over the
commercialization of the Collaboration Products in the United States and, in
such event, the Parties would promptly agree upon a transition plan). In
exercising such authority and control, Bayer shall use the level of efforts and
resources (including the promptness with which such efforts and resources would
be applied) commonly used by Bayer with respect to a product of commercial
potential

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similar to the Collaboration Products at a similar stage in its development or
product life, taking into consideration its safety and efficacy, its cost to
develop, the competitiveness of alternative products of Third Parties, the
patent and other proprietary position of such product, its profitability and all
other relevant factors.
Additionally and in furtherance of Bayer’s exclusive authority and control set
forth in Paragraph 1.a above, during the U.S. Royalty Term, except in the event
that Bayer elects to discontinue commercialization of the Collaboration Products
in the United States and Onyx exercises the right to assume exclusive authority
and control over the commercialization of the Collaboration Products in the
United States, in each case pursuant to Paragraph 1.a above, Bayer shall
control, and be solely responsible for all costs and expenses relating to, sales
of the Collaboration Products in the United States, including, without
limitation: (i) marketing and promotion, (ii) pricing and access and (iii)
medical affairs. For the avoidance of doubt and notwithstanding anything in the
Collaboration Agreement to the contrary, during the U.S. Royalty Term, Bayer
shall be solely responsible for all costs and expenses that are defined as or
deemed “Allowable Co-Promotion Expenses” in the Co-Promotion Agreement,
including, without limitation, all ongoing or future costs and expenses related
to Phase 4 clinical studies in the United States.
b.
The Parties hereby agree that the Executive Committee shall develop a plan for,
and manage, the orderly termination of the co-promotion activities and
arrangements contemplated in the Co-Promotion Agreement on commercially
reasonable terms, provided, however, that all such co-promotion activities and
arrangements shall be fully terminated on or before the Termination Date.

c.
The Parties hereby acknowledge and agree that (i) neither Onyx nor Bayer is a
“Breaching Party” under the Co-Promotion Agreement and the provisions of Section
10.5(c) of the Co-Promotion Agreement shall not apply to the termination of the
Co-Promotion Agreement, (ii) the termination of the Co-Promotion Agreement as
set forth herein shall not release or operate to discharge either Party from any
liability or obligation that may have accrued prior to the Termination Date, and
(iii) from and after the Termination Date, the Co-Promotion Collaboration
Product (as defined in the Co-Promotion Agreement) shall (x) cease to be a
Co-Promoted Product and a Co-Promotion Product and (y) not be deemed a
Royalty-Bearing Product under the Collaboration Agreement.

d.
The Parties hereby acknowledge and agree that, from the date hereof until the
Termination Date, the terms of the Co-Promotion Agreement, including, without
limitation, the terms of Article VIII of the Co-Promotion Agreement (Economics
of Co-Promotion; Profit Sharing), remain in full force and effect. For clarity,
the Parties hereby further acknowledge and agree that each Party shall bear its
own costs and expenses required to implement the terms of this Agreement
(including severance costs related to personnel) and any such costs and expenses
shall not be considered Allowable Co-Promotion Expenses or otherwise shared by
the Parties.

e.
Bayer shall use Commercially Reasonable Efforts to obtain, at its own expense
and in a timely manner, any U.S. Regulatory Approvals that are required by
applicable law to remove the Onyx name and/or logo from the Collaboration
Products’ label, promotional materials and other materials that utilize as of
the date hereof the Onyx name and/or logo . Upon Bayer’s request, Onyx shall
provide Bayer reasonable assistance with obtaining such U.S. Regulatory
Approvals, provided that Bayer shall reimburse Onyx for its reasonable
out-of-pocket expenses in connection therewith.

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With respect to the Collaboration Products’ label, promotional materials and
other materials that utilize as of the date hereof the Onyx name and/or logo
which require U.S. Regulatory Approval in order to remove the Onyx name and/or
logo (as the case may be), Onyx shall permit Bayer to use, manufacture and/or
sell (as the case may be) such material (provided the Bayer name and/or logo are
also used on such materials or label) until depleted, provided, however, that
following receipt of any applicable U.S. Regulatory Approval Bayer shall sell in
a reasonably prompt manner its remaining inventory of Collaboration Products and
use in a reasonably prompt manner its remaining inventory of such promotional
materials and other materials.
With respect to the Collaboration Products’ label, promotional materials and
other materials that utilize as of the date hereof the Onyx name and/or logo
which do not require U.S. Regulatory Approval in order to remove the Onyx name
and/or logo (as the case may be), Onyx shall permit Bayer to use, manufacture
and/or sell (as the case may be) such material (provided the Bayer name and/or
logo are also used on such materials or label) for a period expiring ninety (90)
days after the Termination Date.
From and after the Termination Date, Bayer shall not create any new promotional
or other materials or label for the Collaboration Products that bears the Onyx
name and/or logo.
For purposes of this letter, “Commercially Reasonable Efforts” shall mean: the
level of efforts and resources (including the promptness with which such efforts
and resources would be applied) commonly used in the pharmaceutical industry
with respect to a product of commercial potential similar to the Collaboration
Products at a similar stage in its development or product life, taking into
consideration its safety and efficacy, its cost to develop, the competitiveness
of alternative products of Third Parties, the patent and other proprietary
position of such product, its profitability and all other relevant factors.
f.
The Parties hereby agree that, as has been the agreed-upon practice of the
Parties under the Collaboration Agreement, for purposes of the Parties’
prospective arrangements set forth in this letter, the United States shall refer
to the fifty (50) states of the United States of America and the District of
Columbia, but shall exclude territories and possessions thereof. For the
avoidance of doubt, the United States territories and possessions other than the
fifty (50) states and the District of Columbia shall be treated for all purposes
hereunder in an equivalent manner to any country worldwide other than the United
States and compensation for sales of Collaboration Products in such territories
and possessions shall be governed by Section 16.1 of the Collaboration
Agreement.

2.Promotion of Competing Products. Until the later of (a) the expiration of the
last-to-expire Bayer Patent that includes a Valid Claim that covers
Collaboration Products sold in the United States, or (b) the expiration of
regulatory exclusivity of the Collaboration Products in the United States, the
Bayer sales force responsible for marketing the Collaboration Products in the
United States shall not market a Competing Product (as such term is defined in
the Co-Promotion Agreement) without the prior written consent of Onyx.
Notwithstanding the foregoing, the Parties hereby acknowledge and agree that
each and every product that Bayer commercializes in the United States as of the
date hereof (including, without limitation, Stivarga® (regorafenib)) shall not
be considered a Competing Product for the purposes hereof.
3.Royalties. The Parties hereby agree that, notwithstanding anything in the
Collaboration Agreement to the contrary, the allocation of Marketing Profits and
Marketing Losses set forth in Section 16.1 of the Collaboration Agreement
(including, without limitation, the allocation and/or reimbursement of Allowable
Expenses) shall not apply with respect to the sale of Collaboration Products in
the United

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States during the U.S. Royalty Term. The Parties hereby agree that, during the
U.S. Royalty Term, the exclusive compensation for sales of Collaboration
Products in the United States shall be as follows:
a.
Royalty. Bayer shall pay to Onyx non-refundable, non-creditable royalties equal
to thirty-nine percent (39%) of Net Sales of all Collaboration Products in the
United States during the U.S. Royalty Term. Any sales of Collaboration Products
in the United States by or on behalf of Bayer, its Affiliates, licensees and/or
sublicensees shall be treated hereunder as if such sales were made by Bayer. If
Bayer grants licenses to its Affiliates or Third Parties to make or sell
Collaboration Products in the United States, it shall include an obligation for
such parties to account for and report Net Sales of Collaboration Products on
the same basis as if such sales were made by Bayer, and Bayer shall pay
royalties to Onyx under this letter as if the Net Sales of such Collaboration
Products by such Affiliates and Third Parties were Net Sales of Bayer.
Notwithstanding the foregoing, if during the U.S. Royalty Term, a Third Party
receives marketing authorization for and commences commercial sale of a Generic
Product (as defined below) in the United States, then royalties payable to Onyx
with respect to Net Sales of the applicable Collaboration Product in the United
States shall be reduced to nineteen and one half percent (19.5%) beginning on
the first day of the first full calendar quarter following the date of first
sale of the Generic Product in which Net Sales of the applicable Collaboration
Product in the United States in such calendar quarter decrease by more than
fifty percent (50%) from the Net Sales of such Collaboration Product in the
United States in the calendar quarter immediately preceding the first sale of
such Generic Product. For the purposes of this provision, a “Generic Product”
shall mean, with respect to a Collaboration Product, any pharmaceutical product
in the United States that: (i) contains the same active pharmaceutical
ingredient as the Collaboration Product; (ii) is approved by the FDA in
reliance, in whole or in part, on the prior Drug Approval of such Collaboration
Product (e.g., pursuant to 21 U.S.C. 355(b)(2), an abbreviated new drug
application (ANDA) pursuant to 21 U.S.C. §355(j), a separate NDA, compendia
listing, other Drug Approval Application or otherwise, including foreign
equivalents of the foregoing); (iii) has one or more Governmental or Regulatory
Authority-approved indications in the United States equivalent to the
Governmental or Regulatory Authority-approved indication for such Product in the
United States; (iv) is bioequivalent to such Collaboration Product as determined
by the FDA; and (v) is sold in the United States by a Third Party that (a) is
not a licensee or sublicensee of Bayer or its Affiliates or any of their
licensees or sublicensees, (b) has not obtained such product from a chain of
distribution including Bayer, its Affiliates or any of their licensees or
sublicensees, and (c) is not otherwise authorized by Bayer or any of its
Affiliates, licensees, sublicensees or distributors to sell such product.

b.
U.S. Royalty Term. Royalties shall be paid under this Paragraph 3 during the
period from the Termination Date until the date of the termination or
expiration, as the case may be, of the Collaboration Agreement in accordance
with its terms (such period, the “U.S. Royalty Term”).

c.
Royalty Reports and Payments. Within ten (10) days following the end of each
calendar quarter during the U.S. Royalty Term, Bayer shall provide Onyx with a
report estimating Net Sales of the Collaboration Products in the United States
for such calendar quarter. Within thirty (30) days following the end of each
calendar quarter during the U.S. Royalty Term, Bayer shall provide Onyx with a
report containing the following information for such calendar quarter: (i) the
amount of gross sales of Collaboration Products in the United States, (ii) an
itemized calculation of Net Sales in the United States showing deductions
permitted in the definition of “Net Sales,” and (iii) the calculation of the
royalty payment due on such sales pursuant to Paragraph 3.a hereof. Bayer shall
pay to Onyx all amounts due to Onyx pursuant

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to this Paragraph 3 within forty-five (45) days following the end of each
calendar quarter in which royalties are due under Paragraph 3.a.
d.
Books and Records. During the U.S. Royalty Term, Bayer shall, and shall cause
its Affiliates, licensees and sublicensees to, keep complete and accurate books
and records that disclose the total United States sales and Net Sales of
Collaboration Products in the United States, the number of units of
Collaboration Products sold in the United States, and all matters relating to
those sales that are relevant for the purposes of determining the royalties due
to Onyx hereunder. During the U.S. Royalty Term, Bayer shall, and shall cause
its Affiliates to, (i) maintain such books and records in sufficient detail to
calculate all amounts payable hereunder and to verify compliance with Bayer’s
obligations under this letter, and (ii) retain such books and records until the
later of (a) five (5) years after the end of the period to which such books and
records pertain, and (b) the expiration of the applicable tax statute of
limitation (or any extensions thereof), or for such longer period as may be
required by applicable laws.

e.
Other Royalty Terms. The Parties hereby acknowledge and agree that the terms of
Sections 4.4 (Mode of Payment), 4.5 (Taxes), 4.6 (Interest on Late Payments),
4.7 (Audit), 4.8 (Audit Dispute) and 4.9 (Confidentiality) of the Agreement
Regarding Regorafenib, dated as of October 11, 2011, by and between the Parties,
are incorporated herein mutatis mutantis such that these provisions apply to
sales of Collaboration Products in the United States during the U.S. Royalty
Term and the royalties payable to Onyx under this Paragraph 3 in connection
therewith.

4.Taxes. The Parties hereby affirm and agree that this letter is not intended to
in any way modify the Tax Partnership or the characterization of the
relationship between the Parties for tax purposes as set forth in Section 23 of
the Collaboration Agreement. Without limiting the generality of the foregoing,
royalties paid under Paragraph 3.a hereof shall not be deemed to be distributive
shares of income from the Tax Partnership referred to in Section 23 of the
Collaboration Agreement.
5.Collaboration Agreement.
a.
Governance. Notwithstanding anything set forth in the Collaboration Agreement,
from and after the Termination Date, the Parties shall only be required to
constitute the Alliance Steering Committee (the “ASC”), the Executive Committee
(the “EC”), the Joint Project Committee (the “JPC”) and any subcommittee as
either the ASC or EC shall decide by unanimous written consent. For the
avoidance of doubt, neither the ASC, EC or JPC shall have any responsibility
with respect to, or the right to approve, U.S. marketing activities.

b.
Global Development. Except as expressly set forth in this letter, nothing in
this letter is intended to modify or otherwise alter the provisions of the
Collaboration Agreement with respect to ongoing and / or future global clinical
development of the Collaboration Compounds including provisions related to the
sharing of costs and expenses and decision-making. Global clinical development
projects refer to those development projects approved by the EC and managed
globally even if such development projects may benefit the United States. For
clarity, the Parties hereby acknowledge and agree that (i) the ongoing pediatric
program is considered a global clinical development project for the purposes of
this provision and (ii) the ongoing Phase 4 clinical studies in the United
States are not considered global clinical development projects and Bayer shall
be solely responsible for all costs and expenses relating thereto.

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c.
Separate Development Program. The Parties hereby acknowledge and agree that,
effective as of the Termination Date, Sections 1.86, 1.87 and 12.5 of the
Collaboration Agreement are hereby deleted in their entirety and shall no longer
be of any force or effect.

d.
Co-Promotion Right. The Parties acknowledge and agree that, effective as of the
Termination Date, Sections 13.4, 13.5, 13.6, 13.7, 13.8, 13.9, 13.10 and 13.11
of the Collaboration Agreement are hereby deleted in their entirety and shall no
longer be of any force or effect.

e.
Notice. The addresses to which notices to Bayer pursuant to Section 28.7 of the
Collaboration Agreement shall be addressed shall be:

If to Bayer, addressed to:
Bayer HealthCare LLC
100 Bayer Boulevard
Whippany, New Jersey 09781
Attention: Sr. VP and General Counsel
Facsimile: XXXXXXXXXX
With a copy to:
Bayer HealthCare Pharmaceuticals Inc.
100 Bayer Boulevard
Whippany, New Jersey 09781
Attention: Global Head of Oncology
Facsimile: XXXXXXXXXX
f.
Term and Termination. The Parties acknowledge and agree that Section 24.1(c) of
the Collaboration Agreement is hereby deleted in its entirety and replaced with
the following: “the last date on which any Party or its Affiliates, licensees or
sublicensees markets or sells any Collaboration Product anywhere in the world.”

6.Full Force and Effect. Except as expressly set forth in this letter, the
Collaboration Agreement remains in full force and effect.
7.Miscellaneous. This letter, together with the Collaboration Agreement, as
modified hereby, contains all of the terms agreed to by the Parties regarding
the subject matter of this letter and supersedes any prior oral or written
agreements, understandings or arrangements between the Parties as to the subject
matter hereof. This letter may not be amended, modified, altered or supplemented
except by means of a written agreement or other instrument executed by both
Parties. This letter may be executed in one or more counterparts, each of which
shall be deemed an original, but both of which together shall constitute one and
the same instrument. Each Party may execute this letter by facsimile
transmission or in PDF format sent by electronic mail. Facsimile or PDF
signatures of authorized signatories of the Parties will be deemed to be
original signatures, will be valid and binding upon the Parties and, upon
delivery, will constitute due execution of this letter. This letter shall be
deemed to have been entered into and shall be construed and enforced in
accordance with the laws of the State of California without giving effect to any
choice or conflict of laws provision.

[signature page follows]

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Please confirm that the foregoing is in accordance with your understanding of
our agreement by signing and returning to us a copy of this letter.

Sincerely,

Onyx Pharmaceuticals, Inc.

/s/ SEAN E. HARPER
Name: Sean E. Harper
Title: President

ACKNOWLEDGED AND AGREED:
Bayer HealthCare LLC

/s/ DANIEL APEL
Name: Daniel Apel
Title: President, Bayer HealthCare LLC

Cc:     Bayer HealthCare Pharmaceuticals Inc.
100 Bayer Boulevard
PO Box 915
Whippany, NJ 07981-0915
Attention: Global Head of Oncology
Facsimile: XXXXXXXXXX

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