Exhibit 10.21

[*] Certain information in this document has been omitted and filed separately
with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.

FIRST AMENDMENT TO

DEVELOPMENT, MANUFACTURING, AND SUPPLY AGREEMENT

This first amendment (the “First Amendment”) to DEVELOPMENT, MANUFACTURING, AND
SUPPLY AGREEMENT (the “Agreement”) is made effective as of July 21, 2008, 2008
(the “Amendment Effective Date”) by and between DIADEXUS, INC., organized under
the laws of Delaware and having its principal place of business at 343 Oyster
Point Boulevard, South San Francisco, California 94080, United States of America
(“diaDexus”), and DENKA SEIKEN, organized under the laws of Japan and having its
principal place of business at 3-4-2 Nihonbashi Kayabacho, Chuo-ku, Tokyo
103-0025, Japan (“Denka Seiken”).

WITNESSETH:

WHEREAS, diaDexus and Denka Seiken entered into the DEVELOPMENT, MANUFACTURING,
AND SUPPLY AGREEMENT (the “Agreement”) on March 27th, 2007; and

WHEREAS, diaDexus and Denka Seiken desire to amend the Agreement as set forth
below.

NOW, THEREFORE, in consideration of the promises and undertakings set forth in
this First Amendment, the Parties agree as follows:

 

  1. Any capitalized terms used in this First Amendment, but not defined herein,
shall have the meanings ascribed to them in the Agreement.

 

  2. Exhibit 1.14 shall be replaced with Exhibit 1.14.2 attached to this First
Amendment.

 

  3. Exhibit 1.16 shall be replaced with Exhibit 1.16.2 attached to this First
Amendment.

 

  4.

diaDexus is released from its obligations for the milestone payments stipulated
in Section 3.2 (a) and also from some parts of the milestone payments stipulated
in Section 3.2 (b) as detailed below. Instead diaDexus agrees to pay the total
amount shown in the table in Article 6 as a part of the Transfer Price for the
1st commercial lot of the Product.

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[*]

 

  5.

diaDexus agrees to pay for the validation lots of the Products manufactured by
Denka Seiken according to the Transfer Price stipulated in Section 3.3. With an
assumption that total number of tests to be shipped in the 1st Fiscal Year [*].
The quantities and costs of the validation lots are summarized below. diaDexus
agrees to pay the total amount shown in the table in Article 6 as a part of the
Transfer Price for the 1st commercial lot of the Product. Denka Seiken agrees to
pay for the rare reagents to diaDexus for those used for the validation lots
shown in the following table.

[*]

[*] Certain information in this document has been omitted and filed separately
with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.

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  6. In consideration of Article 4 and Article 5 above, the Transfer Price for
the 1st commercial lot of the Product are determined as shown below. These
prices are applied one time only and only for the 1st commercial lot to be
released [*].

[*]

 

  7. Continuance of Exhibit; Single Document. Except as specifically amended by
this Amendment, all provisions in the Agreement shall remain in full force and
effect. The Agreement, as amended by this Amendment, should hereafter be read as
a single integrated document, incorporating the changes set forth in this
Amendment.

IN WITNESS WHEREOF, diaDexus and DENKA SEIKEN have this Amendment to be executed
by their respective duly authorized officers as of the date first above written.

 

DIADEXUS INC.      DENKA SEIKEN By:   

/s/ P. Plewman

     By:   

/s/ Hiroshi Adachi

Name:   

P. Plewman

     Name:   

Hiroshi Adachi

Title:   

President & CEO

     Title:   

Senior General Manager

Date:   

Jul 21, 2008

     Date:   

July 3, 2008

[*] Certain information in this document has been omitted and filed separately
with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.

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EXHIBIT 1.14.2

PRODUCTS

[*]

[*] Certain information in this document has been omitted and filed separately
with the Securities and Exchange Commission. Confidential treatment has been
requested with respect to the omitted portions.

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EXHIBIT 1.16.2

SPECIFICATION

 

Element

  

Design Inputs

    [*]    [*]

 

[*] Three pages have been omitted and filed separately with the Securities and
Exchange Commission. Confidential treatment has been requested with respect to
the omitted portion.