Exhibit 5.1



                                           September 10, 2003



EXACT Sciences Corporation
100 Campus Drive
Marlborough, MA 01752


         RE:   Form S-3 Universal Shelf Registration Statement Relating to
               $100,000,000 Aggregate Principal Amount of Securities of EXACT
               Sciences Corporation

Dear Sir or Madam:

         We are counsel to EXACT Sciences Corporation, a Delaware corporation
(the "Company"), and have represented the Company in connection with the
preparation and filing with the Securities and Exchange Commission (the
"Commission") of the Company's Registration Statement on Form S-3 (the
"Registration Statement"), on or about the date hereof, covering the proposed
issuance and sale by the Company of up to $100,000,000 of (i) shares of its
common stock, $0.01 par value per share (the "Common Stock"), (ii) shares of its
preferred stock, $0.01 value per share (the "Preferred Stock"), (iii)
debentures, notes, bonds or other evidences of indebtedness of the Company (the
"Debt Securities"), (iv) warrants to purchase shares of Common Stock (the
"Common Stock Warrants"), (v) warrants to purchase shares of Preferred Stock
(the "Preferred Stock Warrants") and (vi) warrants to purchase Debt Securities
(the "Debt Warrants," and together with the Common Stock, Preferred Stock, Debt
Securities, Common Stock Warrants and Preferred Stock Warrants the
"Securities").

         In connection with this opinion, we have examined such corporate
records, documents, instruments, and such questions of law as we have deemed
necessary for the purpose of rendering the opinions set forth herein. We have
also examined the Registration Statement as filed with the Commission in
accordance with the provisions of the Securities Act of 1933, as amended (the
"Securities Act"), and the rules and regulations of the Commission thereunder.

         In such examination, we have assumed the genuineness of all signatures
and the authenticity of all documents submitted to us as originals and the
conformity with originals of all documents submitted to us as copies or
facsimiles.





EXACT Sciences Corporation
September 10, 2003
Page 2


         The opinions hereinafter expressed are subject to the following
qualifications and exceptions: (i) the effect of bankruptcy, insolvency,
reorganization, arrangement, moratorium or other similar laws relating to or
affecting the rights of creditors generally, including without limitation, laws
relating to fraudulent transfers or conveyances, preferences and equitable
subordination; and (ii) limitations imposed by general principles of equity upon
the availability of equitable remedies or the enforcement of provisions of
agreements relating to the Securities, and the effect of judicial decisions that
have held that certain provisions are unenforceable where their enforcement
would violate the implied covenant of good faith and fair dealing, or would be
commercially unreasonable, or where a default under a provision of any agreement
relating to the Securities is not material.

         Based upon and subject to the foregoing, we are of the opinion that:

         1. With respect to the Common Stock, when (a) the Board of Directors of
the Company or a duly authorized committee of the Board of Directors (such Board
of Directors or committee being referred to herein as the "Board"), has taken
all necessary corporate action to approve the issuance of and establish the
terms of the offering of the Common Stock and related matters and (b) issued,
sold and delivered in the manner and for the consideration (not less than the
par value of the Common Stock) stated in the applicable definitive purchase,
underwriting or similar agreement or upon conversion, exchange or exercise of
any other Security in accordance with the terms of such Security or the
instrument governing such Security providing for such conversion, exchange or
exercise as approved by the Board, for the consideration approved by the Board
(not less than the par value of the Common Stock), the Common Stock will be
validly issued, fully paid and nonassessable.

         2. With respect to the Preferred Stock, when (a) the Board has taken
all necessary corporate action to approve the issuance of and establish the
terms of the offering of the Preferred Stock and related matters and (b) issued,
sold and delivered in the manner and for the consideration stated in the
applicable definitive purchase, underwriting or similar agreement or upon
conversion, exchange or exercise of any other Security in accordance with the
terms of such Security or the instrument governing such Security providing for
such conversion, exchange or exercise as approved by the Board, for the
consideration approved by the Board, the Preferred Stock will be validly issued,
fully paid and nonassessable.

         3. With respect to the Debt Securities to be issued under an indenture
(incorporating the form of indenture filed as Exhibit 4.03 to the Registration
Statement or such other provisions as are contained in a document which will be
filed as an exhibit or incorporated by reference in the Registration Statement)
(the "Indenture"), when (a) the Indenture has been (i) duly authorized by the
Board, (ii) duly executed and delivered by





EXACT Sciences Corporation
September 10, 2003
Page 3


each party thereto and (iii) duly qualified under the Trust Indenture Act of
1939, as amended, (b) the Board has taken all necessary corporate action to
approve the issuance of and establish the terms of such Debt Securities, the
terms of the offering and related matters, (c) the Debt Securities have been
executed and authenticated in accordance with the terms of the Indenture and (d)
the Debt Securities have been issued, sold and delivered in the manner and for
the consideration stated in the applicable definitive purchase, underwriting or
similar agreement approved by the Board, upon payment of the consideration
provided for therein, or upon exercise of any other Security in accordance with
the terms of such Security or the instrument governing such Security providing
for such conversion, exchange or exercise as approved by the Board, and the
Indenture, the Debt Securities to be issued under the Indenture will be valid
and binding obligations of the Company, enforceable against the Company in
accordance with their respective terms.

         4. With respect to the Common Stock Warrants, when (a) one or more
agreements (incorporating the provisions as are contained in a document which
will be filed as an exhibit to or incorporated by reference in the Registration
Statement) have been duly executed and delivered by the Company and a warrant
agent, (b) the Board has taken all necessary corporate action to approve the
terms of the Common Stock Warrants, (c) the Common Stock Warrants have been
executed in accordance with the terms of the appropriate agreement and (d) the
Common Stock Warrants have been issued, sold and delivered in the manner and for
the consideration stated in the applicable definitive purchase, underwriting or
similar agreement approved by the Board, upon payment of the consideration
therefor provided for therein, the Common Stock Warrants will be binding
obligations of the Company under Massachusetts law and the securities issuable
upon exercise thereof will be validly issued, fully paid and nonassessable.

         5. With respect to the Preferred Stock Warrants, when (a) one or more
agreements (incorporating the provisions as are contained in a document which
will be filed as an exhibit to or incorporated by reference in the Registration
Statement) have been duly executed and delivered by the Company and a warrant
agent, (b) the Board has taken all necessary corporate action to approve the
terms of the Preferred Stock Warrants, (c) the Preferred Stock Warrants have
been executed and authenticated in accordance with the terms of the appropriate
agreement and (d) the Preferred Stock Warrants have been issued, sold and
delivered in the manner and for the consideration stated in the applicable
definitive purchase, underwriting or similar agreement approved by the Board,
upon payment of the consideration therefor provided for therein, the Preferred
Stock Warrants will be binding obligations of the Company under Massachusetts
law and the securities issuable upon exercise thereof will be validly issued,
fully paid and nonassessable.





EXACT Sciences Corporation
September 10, 2003
Page 4


         6. With respect to the Debt Warrants, when (a) one or more agreements
(incorporating the provisions as are contained in a document which will be filed
as an exhibit to or incorporated by reference in the Registration Statement)
have been duly executed and delivered by the Company and a warrant agent, (b)
the Board has taken all necessary corporate action to approve the terms of the
Debt Warrants, (c) the Debt Warrants have been executed and authenticated in
accordance with the terms of the appropriate agreement and (d) the Debt Warrants
have been issued, sold and delivered in the manner and for the consideration
stated in the applicable definitive purchase, underwriting or similar agreement
approved by the Board, upon payment of the consideration therefor provided for
therein, the Debt Warrants will be binding obligations of the Company under
Massachusetts law and the securities issuable upon exercise thereof will be
validly issued, fully paid and nonassessable.

         In connection with our opinions expressed above, we have assumed that,
at or prior to the time of the delivery of any such Security, the Registration
Statement, and any amendments thereto (including post-effective amendments) will
have been declared effective, a prospectus supplement will have been prepared
and filed with the Commission describing the Securities offered thereby, the
authorization of the Securities applicable to such Security will not have been
modified or rescinded by the Board and there will not have occurred any change
in law affecting the validity or enforceability of such Security. We have also
assumed that none of the terms of any Security to be established subsequent to
the date hereof nor the issuance and delivery of such Security, nor the
compliance by the Company with the terms of such Security, will violate any
applicable federal or state law or will result in a violation of any provision
of any instrument or agreement then binding upon the Company or any restriction
imposed by any court or governmental body having jurisdiction over the Company.

         This opinion is based upon currently existing statutes, rules,
regulations and judicial decisions, and we disclaim any obligation to advise you
of any change in any of these sources of law or subsequent legal or factual
developments which might affect any matters or opinions set forth herein.





EXACT Sciences Corporation
September 10, 2003
Page 5


         We hereby consent to the filing of this opinion with the Commission in
connection with the filing of the Registration Statement. We also consent to the
use of our name in the related prospectus and any related prospectus supplement
under the heading "Legal Matters." In giving this consent, we do not thereby
admit that we are included in the category of persons whose consent is required
under Section 7 of the Securities Act or the rules and regulations promulgated
thereunder.


                                Very truly yours,

                                /s/ TESTA, HURWITZ & THIBEAULT, LLP

                                TESTA, HURWITZ & THIBEAULT, LLP