[HOLOGIC LETTERHEAD]

Exhibit 10.4

May 20, 2007

Robert A. Cascella

Chief Operating Officer

Hologic, Inc.

Dear Rob,

Reference is made to the transactions contemplated by that certain Agreement and
Plan of Merger by and among Hologic, Inc. (the “Company”), Nor’easter Corp. and
Cytyc Corporation (“Cytyc”) dated as of May 20, 2007 (the “Merger Agreement”).
Reference is also made to that certain Amended and Restated Change of Control
Agreement, dated October 30, 2006 (the “Change of Control Agreement”) between
the Company and you.

The Company hereby acknowledges and agrees that the merger contemplated by the
Merger Agreement (the “Merger”), pursuant to which the stockholders of Cytyc
will receive over 50% of the outstanding shares of the Company would constitute
a change of control under the Change of Control Agreement and certain other
plans and/or agreements pursuant to which you were granted stock options and
restricted stock units (“Equity Award Agreements”).

Concurrent with the execution of the Merger Agreement and subject to
consummation of the Merger, you agreed to waive certain rights under your Change
of Control Agreement and certain Equity Award Agreement pursuant to a letter
dated May 20, 2007. In exchange for such waiver and in consideration of your
continued employment by the Company and subject to the Merger, the Board of
Directors of the Company has approved a new retention agreement whereby you will
be eligible to receive a retention bonus (the “Retention Bonus”) of Two Million
Dollars ($2,000,000.00) as described in the attached Term Sheet. In the event
that the Merger Agreement is terminated prior to the Effective Time (as that
term is defined in the Merger Agreement), this letter and the retention bonus
shall become null and void ab initio and be of no further force and effect.

Except as expressly set forth herein, this letter does not affect the terms or
in any way waive any other rights that you may have under the Retention and
Severance Agreement dated May 3, 2006, Supplemental Executive Retirement Plan,
Restricted Stock Unit Agreements, if applicable, Amended and Restated 1999
Equity Incentive Plan and options issued thereunder or any other agreements
between you and the Company or the compensation and benefit plans of the Company
in which you participate.

 

Very truly yours, Hologic, Inc. By:  

/s/ John W. Cumming

Name:   John W. Cumming Title:   Chief Executive Officer

Enclosure: Principal Terms of Proposed Retention Agreement

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HOLOGIC, INC.

PRINCIPAL TERMS

PROPOSED RETENTION AGREEMENT

with

Robert A. Cascella

 

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May 16, 2007

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PRINCIPAL TERMS OF

PROPOSED RETENTION AGREEMENT

 

Existing Change of Control Agreement    Mr. Cascella shall waive and release his
right to change of control payment and special bonus under his existing Amended
and Restated Change of Control Agreement upon consummation of the Cytyc
transaction. In the event Mr. Cascella is terminated without Cause or resigns
for Good Reason within two years following the closing of the Cytyc transaction,
then he is entitled to immediate payout of his change of control payment (3 x
base salary and highest bonus) and special bonus (1 x base salary and highest
bonus). The existing change of control agreement shall remain in place. Existing
Retention and Severance Agreement    The existing Retention and Severance
Agreement, dated as of May 3, 2006, shall remain in place. Term of Retention
Agreement    Three year term providing Mr. Cascella with a Retention Bonus if he
remains employed with the Company or its successor through the Retention Date.
Retention Date    The three year anniversary of the closing of the transaction,
with no payment for termination prior to the Retention Date for any reason,
except resignation for Good Reason or termination without Cause. Retention Bonus
   Mr. Cascella shall receive a Retention Bonus in an amount equal to
approximately $2,000,000. The Retention Bonus will be paid 50% in cash and 50%
in Restricted Stock Units, subject to normal tax withholding, payable upon the
Retention Date. Accelerated Retention Bonus for Without Cause Termination or
Resignation for Good Reason.    If Company terminates Mr. Cascella without
“Cause” or he resigns for “Good Reason,” then the Retention Bonus shall be paid
immediately. Cause   

Cause is defined as:

 

(i) any acts or personal dishonesty taken by Mr. Cascella and intended to result
in substantial personal enrichment of Mr. Cascella at the expense of the
Company;

 

(ii) material violation of the Company’s code of conduct and other Company Codes
of Conduct or policies and procedures that are applicable to Mr. Cascella; or

 

(iii) conviction of Mr. Cascella of felony involving moral turpitude.

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   The Company must provide Mr. Cascella with 30 days written notice of any
determination of cause and provide Mr. Cascella for a period of 30 days
following such notice with the opportunity to appear before the Board with or
without legal representation to present arguments and evidence on his behalf.
Further, Mr. Cascella may only be terminated for a cause if the Board
determines, by a vote of at least 75% of the independent directors that his
actions did, in fact, constitute for Cause. Good Reason   

Good reason means:

 

(i) material diminution in Mr. Cascella’s authority, duties or responsibilities;

 

(ii) ceases to report to Hologic CEO;

 

(iii) any person other than Jack Cumming serves as CEO of Hologic; and

 

(iv) material breach by the Company of the Retention Agreement.

 

The Executive must provide notice to the Company of the alleged occurrence of
any of the above within thirty (30) days of occurrence and the Company has
thirty (30) days to remedy the condition.

Change of Control Agreement    Retention payments provided hereunder shall be
excluded from the calculation of change of control payment and special bonus
payment provided for under the Amended and Restated Change of Control Agreement.