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                                                                   Exhibit 10.27


[INCYTEGENOMICS LETTERHEAD]


October 18, 2001

Patrick Plewman
Chief Executive Officer
diaDexus, Inc.
343 Oyster Point Blvd.
South San Francisco, CA 94080


Dear Patrick:

This letter is intended to amend and clarify the Collaborative Agreement (the
"Agreement"), effective as of September 2, 1997 entered into by and between
diaDexus, Inc., a Delaware corporation having its principal place of business
at 343 Oyster Point Blvd., South San Francisco, California 94080, the successor
in interest to diaDexus LLC ("diaDexus"), and Incyte Genomics, Inc., a Delaware
corporation having its principal place of business at 3160 Porter Drive, Palo
Alto, California 94304, the successor in interest to Incyte Pharmaceuticals,
Inc. ("Incyte").

All capitalized terms not defined in this letter shall have the meaning set
forth in the Agreement.

1.   All references to Incyte Pharmaceuticals in the Agreement are replaced
with Incyte Genomics as the successor in interest to Incyte Pharmaceuticals and
all references to diaDexus, LLC are replaced with diaDexus, Inc. as the
successor in interest to diaDexus, LLC.

2.   Paragraph 3.6(b), line 6, is hereby amended to add the phrase "and
3.6(d)," after the phrase "and 3.4.2(d) with respect to exclusive licenses
granted".

3.   A new Paragraph 3.6(d) is hereby added as follows:

(d)  Sublicensing Drug Product(s) to Third Party Collaborators.
     ----------------------------------------------------------

     On an individual Drug Product-by-Drug Product basis, diaDexus may grant a
     sublicense to any third party under the rights granted to diaDexus
     hereunder with
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     respect to any Drug Product(s), including without limitation with respect
     to the Incyte Database Technology relating to such Drug Product(s), to
     clinically develop, make, use, offer to sell, sell, import, export and
     distribute such Drug Product; provided that (i) such Drug Product(s) is the
     subject of an Investigational New Drug application submitted to the United
     States Food and Drug Administration or an equivalent thereto to any agency,
     (ii) diaDexus has paid Incyte the IND (or equivalent) milestone payment in
     accordance with Section 4.2 prior to grant of such sublicense, (iii) any
     such sublicense is granted together with a grant of rights under
     intellectual property, owned or otherwise held by diaDexus, relating to
     such Drug Product(s) acquired as a result of research and development by or
     on behalf of diaDexus, and (iv) sublicensing rights are provided solely
     with respect to those rights which Incyte has the right to grant diaDexus;
     and (v) sublicensing rights may be granted solely to the extent that such
     sublicense is required by such third party in order to clinically develop,
     make, use, sell, offer to sell, import, export or distribute such diaDexus
     Product, (vi) diaDexus shall be responsible for any and all milestone
     payments and royalties due to Incyte pursuant to Article 4.0 as a
     consequence of such sublicense. diaDexus shall obtain the written
     commitment of any sublicensee to abide by all applicable terms and
     conditions of this Agreement. Promptly upon execution of any permitted
     sublicense, diaDexus shall provide notice thereof to Incyte and reasonable
     satisfactory evidence that such sublicense is in compliance with this
     Section 3.6.

     Any sublicensing outside of (i)-(iv) above, except as otherwise expressly
     provided in this Agreement, is strictly prohibited, including without
     limitation any rights to sublicense Gene Product(s) for use as research
     tools or in database products.

4.   Incyte agrees that diaDexus, pursuant to Section 5.3, may utilize
consultants, academic collaborators and third party collaborators that may or
may not be LifeSeq subscribers (individually and collectively "Collaborators")
to conduct research and development with respect to Designated Gene Products,
including without limitation Designated Gene Products subject to an option
pursuant to Sections 3.4.1 or Section 3.4.2, to discover and evaluate Drug
Products, Antisense Products and Therapeutic Protein Products. Incyte further
agrees that diaDexus may agree to grant a sublicense to Collaborators with
respect to (1) any Drug Product discovered as a result of a collaboration with
such Collaborators in accordance with Section 3.6(b) or Section 3.6(d), and
other applicable provisions of the Agreement, and (2) any Antisense Products or
Therapeutic Protein Products discovered as a result of a collaboration with such
Collaborators in accordance with Sections 3.6(b), and other applicable
provisions of the Agreement.
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Any and all provisions of the Agreement not expressly modified by this letter
shall remain in full force and effect.


Sincerely,



Incyte Genomics, Inc.


By signing this letter, the parties have executed an amendment to the Agreement
effective as of the Effective Date.


DIADEXUS, INC.


By:  /s/ Patrick Plewman
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Name:  Patrick Plewman
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Title:   President & CEO
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Date:    10/18/01
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