SENORX, INC. EMPLOYEE STOCK PURCHASE PLAN

Exhibit 10.4

SENORX, INC.

EMPLOYEE STOCK PURCHASE PLAN

1. Purpose. The purpose of the Plan is to provide employees of the Company and its Designated Subsidiaries with an opportunity to purchase Common Stock of the Company through accumulated payroll deductions. It is the intention of the Company to have the Plan qualify as an “Employee Stock Purchase Plan” under Section 423 of the Code. The provisions of the Plan, accordingly, shall be construed so as to extend and limit participation in a uniform and nondiscriminatory basis consistent with the requirements of Section 423.

2. Definitions.

(a) “Administrator” shall mean the Board or any Committee designated by the Board to administer the plan pursuant to Section 14.

(b) “Board” shall mean the Board of Directors of the Company.

(c) “Change in Control” means the occurrence of any of the following events:

(i) Any “person” (as such term is used in Sections 13(d) and 14(d) of the Exchange Act) becomes the “beneficial owner” (as defined in Rule 13d-3 of the Exchange Act), directly or indirectly, of securities of the Company representing fifty percent (50%) or more of the total voting power represented by the Company’s then outstanding voting securities; or

(ii) The consummation of the sale or disposition by the Company of all or substantially all of the Company’s assets; or

(iii) A change in the composition of the Board occurring within a two-year period, as a result of which fewer than a majority of the directors are Incumbent Directors. “Incumbent Directors” means directors who either (A) are Directors as of the effective date of the Plan, or (B) are elected, or nominated for election, to the Board with the affirmative votes of at least a majority of the Directors at the time of such election or nomination (but will not include an individual whose election or nomination is in connection with an actual or threatened proxy contest relating to the election of directors to the Company); or

(iv) The consummation of a merger or consolidation of the Company with any other corporation, other than a merger or consolidation which would result in the voting securities of the Company outstanding immediately prior thereto continuing to represent (either by remaining outstanding or by being converted into voting securities of the surviving entity or its parent) at least fifty percent (50%) of the total voting power represented by the voting securities of the Company or such surviving entity or its parent outstanding immediately after such merger or consolidation.

(d) “Code” shall mean the Internal Revenue Code of 1986, as amended.

(e) “Committee” means a committee of the Board appointed in accordance with Section 14 hereof.

(f) “Common Stock” shall mean the common stock of the Company.

(g) “Company” shall mean SenoRx, Inc., a Delaware corporation.

(h) “Compensation” shall mean all base straight time gross earnings, commissions, overtime and shift premium, but exclusive of payments for incentive compensation, bonuses and other compensation.

(i) “Designated Subsidiary” shall mean any Subsidiary selected by the Administrator as eligible to participate in the Plan.

(j) “Director” shall mean a member of the Board.

(k) “Eligible Employee” shall mean any individual who is a common law employee of the Company or any Designated Subsidiary and whose customary employment with the Company or Designated Subsidiary is at least twenty (20) hours per week and more than five (5) months in any calendar year. For purposes of the Plan, the employment relationship shall be treated as continuing intact while the individual is on sick leave or other leave of absence approved by the Company. Where the period of leave exceeds 90 days and the individual’s right to reemployment is not guaranteed either by statute or by contract, the employment relationship shall be deemed to have terminated on the 91st day of such leave.

(l) “Exchange Act” shall mean the Securities Exchange Act of 1934, as amended.

(m) “Exercise Date” shall mean the first Trading Day on or after March 31^st and September 30^th of each year. The first Exercise Date under the Plan shall be March 31, 2007.

(n) “Fair Market Value” shall mean, as of any date and unless the Administrator determines otherwise, the value of Common Stock determined as follows:

(i) If the Common Stock is listed on any established stock exchange or a national market system, including without limitation the Nasdaq National Market, its Fair Market Value shall be the closing sales price for such stock (or the closing bid, if no sales were reported) as quoted on such exchange or system on the date of determination, as reported in The Wall Street Journal or such other source as the Board deems reliable;

(ii) If the Common Stock is regularly quoted by a recognized securities dealer but selling prices are not reported, its Fair Market Value shall be the mean of the closing bid and asked prices for the Common Stock on the date of determination, as reported in The Wall Street Journal or such other source as the Board deems reliable;

(iii) In the absence of an established market for the Common Stock, the Fair Market Value thereof shall be determined in good faith by the Board; or

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(iv) For purposes of the Offering Date of the first Offering Period under the Plan, the Fair Market Value shall be the initial price to the public as set forth in the final prospectus included within the registration statement on Form S-1 filed with the Securities and Exchange Commission for the initial public offering of the Company’s Common Stock (the “Registration Statement”).

(o) “Fiscal Year” means the fiscal year of the Company.

(p) “Offering Date” shall mean the first Trading Day of each Offering Period.

(q) “Offering Periods” shall mean the periods of approximately six (6) months during which an option granted pursuant to the Plan may be exercised, commencing on the first Trading Day on or after April 1^st and October 1^st of each year and terminating on the first Trading Day on or after the subsequent Offering Period commencement date approximately six months later; provided, however, that the first Offering Period under the Plan shall commence with the first Trading Day on or after the date on which the Securities and Exchange Commission declares the Company’s registration statement on Form S-1 effective and end on the first Trading Day on or after March 31, 2007 and the second Offering Period under the Plan shall commence with the first Trading Day on or after April 1, 2007. The duration and timing of Offering Periods may be changed pursuant to Section 4 of this Plan.

(r) “Plan” shall mean this SenoRx, Inc. Employee Stock Purchase Plan.

(s) “Purchase Price” shall mean 85% of the Fair Market Value of a share of Common Stock on the Exercise Date; provided however, that the Purchase Price may be determined for subsequent Offering Periods by the Administrator subject to compliance with Section 423 of the Code (or any successor rule or provision or any other applicable law, regulation or stock exchange rule) or pursuant to Section 20.

(t) “Subsidiary” shall mean a “subsidiary corporation,” whether now or hereafter existing, as defined in Section 424(f) of the Code.

(u) “Trading Day” shall mean a day on which the national stock exchange upon which the Company Common Stock is listed is open for trading.

3. Eligibility.

(a) First Offering Period. Any individual who is an Eligible Employee immediately prior to the first Offering Period shall be automatically enrolled in the first Offering Period.

(b) Subsequent Offering Periods. Any Eligible Employee on a given Offering Date shall be eligible to participate in the Plan.

(c) Limitations. Any provisions of the Plan to the contrary notwithstanding, no Eligible Employee shall be granted an option under the Plan (i) to the extent that, immediately after the grant, such Eligible Employee (or any other person whose stock would be attributed to such Eligible Employee pursuant to Section 424(d) of the Code) would own capital stock of the Company

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and/or hold outstanding options to purchase such stock possessing five percent (5%) or more of the total combined voting power or value of all classes of the capital stock of the Company or of any Subsidiary, or (ii) to the extent that his or her rights to purchase stock under all employee stock purchase plans of the Company and its subsidiaries accrues at a rate which exceeds Twenty-Five Thousand Dollars ($25,000) worth of stock (determined at the fair market value of the shares at the time such option is granted) for each calendar year in which such option is outstanding at any time.

4. Offering Periods. The Plan shall be implemented by consecutive Offering Periods with a new Offering Period commencing on the first Trading Day on or after April 1^st and October 1^st each year, or on such other date as the Board shall determine; provided, however, that the first Offering Period under the Plan shall commence with the first Trading Day on or after the date upon which the Company’s Registration Statement is declared effective by the Securities and Exchange Commission and end on the first Trading Day on or after March 31, 2007. The Board shall have the power to change the duration of Offering Periods (including the commencement dates thereof) with respect to future offerings without stockholder approval if such change is announced prior to the scheduled beginning of the first Offering Period to be affected thereafter.

5. Participation.

(a) First Offering Period. An Eligible Employee shall be entitled to participate in the first Offering Period only if such individual submits a subscription agreement authorizing payroll deductions in a form determined by the Administrator (which may be similar to the form attached hereto as Exhibit A) to the Company’s designated plan administrator (i) no earlier than the effective date of the Form S-8 registration statement with respect to the issuance of Common Stock under this Plan and (ii) no later than twenty (20) business days following the effective date of such S-8 registration statement (the “Enrollment Window”). An Eligible Employee’s failure to submit the subscription agreement during the Enrollment Window shall result in the automatic termination of such individual’s participation in the Offering Period.

(b) Subsequent Offering Periods. An Eligible Employee may become a participant in the Plan by completing a subscription agreement in a form determined by the Administrator (which may be similar to the form attached hereto as Exhibit A) and filing it with the Company’s designated Plan administrator prior to the applicable Offering Date.

6. Payroll Deductions.

(a) At the time a participant files his or her subscription agreement, he or she shall elect to have payroll deductions made on each pay day during the Offering Period in an amount not exceeding 10% of the Compensation which he or she receives on each pay day during the Offering Period; provided, however, that should a pay day occur on an Exercise Date, a participant shall have the payroll deductions made on such day applied to his or her account under the new Offering Period. A participant’s subscription agreement shall remain in effect for successive Offering Periods unless terminated as provided in Section 10 hereof.

(b) Payroll deductions for a participant shall commence on the first pay day following the Offering Date and shall end on the last pay day in the Offering Period to which such authorization is applicable, unless sooner terminated by the participant as provided in Section 10

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hereof; provided, however, that for the first Offering Period, payroll deductions shall commence on the first pay day on or following the end of the Enrollment Window.

(c) All payroll deductions made for a participant shall be credited to his or her account under the Plan and shall be withheld in whole percentages only. A participant may not make any additional payments into such account.

(d) A participant may discontinue his or her participation in the Plan as provided in Section 10 hereof, or may increase or decrease the rate of his or her payroll deductions during the Offering Period by completing or filing with the Company a new subscription agreement authorizing a change in payroll deduction rate. The Administrator may, in its discretion, limit the nature and/or number of participation rate changes during any Offering Period. The change in rate shall be effective with the first full payroll period following five (5) business days after the Company’s receipt of the new subscription agreement unless the Company elects to process a given change in participation more quickly.

(e) Notwithstanding the foregoing, to the extent necessary to comply with Section 423(b)(8) of the Code and Section 3(c) hereof, a participant’s payroll deductions may be decreased to zero percent (0%) at any time during an Offering Period. Payroll deductions shall recommence at the rate provided in such participant’s subscription agreement at the beginning of the first Offering Period which is scheduled to end in the following calendar year, unless terminated by the participant as provided in Section 10 hereof.

(f) At the time the option is exercised, in whole or in part, or at the time some or all of the Company’s Common Stock issued under the Plan is disposed of, the participant must make adequate provision for the Company’s or its Subsidiary’s federal, state, or any other tax liability payable to any authority, national insurance, social security or other tax withholding obligations, if any, which arise upon the exercise of the option or the disposition of the Common Stock. At any time, the Company or its Subsidiary may, but shall not be obligated to, withhold from the participant’s compensation the amount necessary for the Company or its Subsidiary to meet applicable withholding obligations, including any withholding required to make available to the Company or its Subsidiary any tax deductions or benefits attributable to sale or early disposition of Common Stock by the Eligible Employee.

7. Grant of Option. On the Offering Date of each Offering Period, each Eligible Employee participating in such Offering Period shall be granted an option to purchase on each Exercise Date during such Offering Period (at the applicable Purchase Price) up to a number of shares of the Company’s Common Stock determined by dividing such Eligible Employee’s payroll deductions accumulated prior to such Exercise Date by the applicable Purchase Price; provided that in no event shall an Eligible Employee be permitted to purchase during each Offering Period more than 1,000 shares of the Company’s Common Stock (subject to any adjustment pursuant to Section 19), and provided further that such purchase shall be subject to the limitations set forth in Sections 3(c) and 13 hereof. The Eligible Employee may accept the grant of such option by turning in a completed Subscription Agreement (attached hereto as Exhibit A) to the Company on or prior to an Offering Date, or with respect to the first Offering Period, prior to the last day of the Enrollment Window. The Administrator may, for future Offering Periods, increase or decrease, in its absolute discretion, the maximum number of shares of the Company’s Common Stock an Eligible Employee may

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purchase during each Offering Period. Exercise of the option shall occur as provided in Section 8 hereof, unless the participant has withdrawn pursuant to Section 10 hereof. The option shall expire on the last day of the Offering Period.

8. Exercise of Option.

(a) Unless a participant withdraws from the Plan as provided in Section 10 hereof, his or her option for the purchase of shares shall be exercised automatically on the Exercise Date, and the maximum number of full shares subject to option shall be purchased for such participant at the applicable Purchase Price with the accumulated payroll deductions in his or her account. No fractional shares shall be purchased; any payroll deductions accumulated in a participant’s account which are not sufficient to purchase a full share shall be retained in the participant’s account for the subsequent Offering Period, subject to earlier withdrawal by the participant as provided in Section 10 hereof. Any other funds left over in a participant’s account after the Exercise Date shall be returned to the participant. During a participant’s lifetime, a participant’s option to purchase shares hereunder is exercisable only by him or her.

(b) If the Administrator determines that, on a given Exercise Date, the number of shares with respect to which options are to be exercised may exceed (i) the number of shares of Common Stock that were available for sale under the Plan on the Offering Date of the applicable Offering Period, or (ii) the number of shares available for sale under the Plan on such Exercise Date, the Administrator may in its sole discretion provide that the Company shall make a pro rata allocation of the shares of Common Stock available for purchase on such Exercise Date in as uniform a manner as shall be practicable and as it shall determine in its sole discretion to be equitable among all participants exercising options to purchase Common Stock on such Exercise Date. The Company may make a pro rata allocation of the shares available on the Offering Date of any applicable Offering Period pursuant to the preceding sentence, notwithstanding any authorization of additional shares for issuance under the Plan by the Company’s stockholders subsequent to such Offering Date.

9. Delivery. As soon as reasonably practicable after each Exercise Date on which a purchase of shares occurs, the Company shall arrange the delivery to each participant the shares purchased upon exercise of his or her option in a form determined by the Administrator.

10. Withdrawal.

(a) A participant may withdraw all but not less than all the payroll deductions credited to his or her account and not yet used to exercise his or her option under the Plan at any time by giving written notice to the Company in the form determined by the Administrator (which may be similar to the form attached as Exhibit B to this Plan). All of the participant’s payroll deductions credited to his or her account shall be paid to such participant promptly after receipt of notice of withdrawal and such participant’s option for the Offering Period shall be automatically terminated, and no further payroll deductions for the purchase of shares shall be made for such Offering Period. If a participant withdraws from an Offering Period, payroll deductions shall not resume at the beginning of the succeeding Offering Period unless the participant delivers to the Company a new subscription agreement.

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(b) A participant’s withdrawal from an Offering Period shall not have any effect upon his or her eligibility to participate in any similar plan which may hereafter be adopted by the Company or in succeeding Offering Periods which commence after the termination of the Offering Period from which the participant withdraws.

11. Termination of Employment. Upon a participant’s ceasing to be an Eligible Employee, for any reason, he or she shall be deemed to have elected to withdraw from the Plan and the payroll deductions credited to such participant’s account during the Offering Period but not yet used to purchase shares of Common Stock under the Plan shall be returned to such participant or, in the case of his or her death, to the person or persons entitled thereto under Section 15, and such participant’s option shall be automatically terminated.

12. Interest. No interest shall accrue on the payroll deductions of a participant in the Plan.

13. Stock.

(a) Subject to adjustment upon changes in capitalization of the Company as provided in Section 19 hereof, the maximum number of shares of the Company’s Common Stock which shall be made available for sale under the Plan shall be 550,000 shares.

(b) Until the shares are issued (as evidenced by the appropriate entry on the books of the Company or of a duly authorized transfer agent of the Company), a participant shall only have the rights of an unsecured creditor with respect to such shares, and no right to vote or receive dividends or any other rights as a stockholder shall exist with respect to such shares.

(c) Shares to be delivered to a participant under the Plan shall be registered in the name of the participant or in the name of the participant and his or her spouse.

14. Administration. The Plan will be administered by an Administrator which shall be either (A) the Board or (B) a Committee appointed by the Board, which committee will be constituted to satisfy all applicable law. The Administrator shall administer the Plan and shall have full and exclusive discretionary authority to construe, interpret and apply the terms of the Plan, to determine eligibility and to adjudicate all disputed claims filed under the Plan. Every finding, decision and determination made by the Administrator shall, to the full extent permitted by law, be final and binding upon all parties. Notwithstanding any provision to the contrary in this Plan, the Administrator may adopt rules or procedures relating to the operation and administration of the Plan to accommodate the specific requirements of local laws and procedures for jurisdictions outside of the United States. Without limiting the generality of the foregoing, the Administrator is specifically authorized to adopt rules and procedures regarding eligibility to participate, the definition of Compensation, handling of payroll deductions, making of contributions to the Plan (including, without limitation, in forms other than payroll deductions), establishment of bank or trust accounts to hold payroll deductions, payment of interest, conversion of local currency, obligations to pay payroll tax, determination of beneficiary designation requirements, withholding procedures and handling of stock certificates which vary with local requirements.

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15. Designation of Beneficiary.

(a) A participant may file a designation of a beneficiary who is to receive any shares and cash, if any, from the participant’s account under the Plan in the event of such participant’s death subsequent to an Exercise Date on which the option is exercised but prior to delivery to such participant of such shares and cash. In addition, a participant may file a designation of a beneficiary who is to receive any cash from the participant’s account under the Plan in the event of such participant’s death prior to exercise of the option. If a participant is married and the designated beneficiary is not the spouse, spousal consent shall be required for such designation to be effective.

(b) Such designation of beneficiary may be changed by the participant at any time by notice in a form determined by the Administrator. In the event of the death of a participant and in the absence of a beneficiary validly designated under the Plan who is living at the time of such participant’s death, the Company shall deliver such shares and/or cash to the executor or administrator of the estate of the participant, or if no such executor or administrator has been appointed (to the knowledge of the Company), the Company, in its discretion, may deliver such shares and/or cash to the spouse or to any one or more dependents or relatives of the participant, or if no spouse, dependent or relative is known to the Company, then to such other person as the Company may designate.

(c) All beneficiary designations shall be in such form and manner as the Administrator may designate from time to time.

16. Transferability. Neither payroll deductions credited to a participant’s account nor any rights with regard to the exercise of an option or to receive shares under the Plan may be assigned, transferred, pledged or otherwise disposed of in any way (other than by will, the laws of descent and distribution or as provided in Section 15 hereof) by the participant. Any such attempt at assignment, transfer, pledge or other disposition shall be without effect, except that the Company may treat such act as an election to withdraw funds from an Offering Period in accordance with Section 10 hereof.

17. Use of Funds. All payroll deductions received or held by the Company under the Plan may be used by the Company for any corporate purpose, and the Company shall not be obligated to segregate such payroll deductions. Until shares are issued, participants shall only have the rights of an unsecured creditor.

18. Reports. Individual accounts shall be maintained for each participant in the Plan. Statements of account shall be given to participating Eligible Employees at least annually, which statements shall set forth the amounts of payroll deductions, the Purchase Price, the number of shares purchased and the remaining cash balance, if any.

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19. Adjustments Upon Changes in Capitalization, Dissolution, Liquidation, Merger or Change in Control.

(a) Changes in Capitalization. Subject to any required action by the stockholders of the Company, the maximum number of shares of the Company’s Common Stock which shall be made available for sale under the Plan, the maximum number of shares each participant may purchase each Offering Period (pursuant to Section 7), as well as the price per share and the number of shares of Common Stock covered by each option under the Plan which has not yet been exercised shall be proportionately adjusted for any increase or decrease in the number of issued shares of Common Stock resulting from a stock split, reverse stock split, stock dividend, combination or reclassification of the Common Stock, or any other change in the number of shares of Common Stock effected without receipt of consideration by the Company; provided, however, that conversion of any convertible securities of the Company shall not be deemed to have been “effected without receipt of consideration.” Such adjustment shall be made by the Administrator, whose determination in that respect shall be final, binding and conclusive. Except as expressly provided herein, no issuance by the Company of shares of stock of any class, or securities convertible into shares of stock of any class, shall affect, and no adjustment by reason thereof shall be made with respect to, the number or price of shares of Common Stock subject to an option.

(b) Dissolution or Liquidation. In the event of the proposed dissolution or liquidation of the Company, the Offering Period then in progress shall be shortened by setting a new Exercise Date (the “New Exercise Date”), and shall terminate immediately prior to the consummation of such proposed dissolution or liquidation, unless provided otherwise by the Administrator. The New Exercise Date shall be before the date of the Company’s proposed dissolution or liquidation. The Administrator shall notify each participant in writing, at least ten (10) business days prior to the New Exercise Date, that the Exercise Date for the participant’s option has been changed to the New Exercise Date and that the participant’s option shall be exercised automatically on the New Exercise Date, unless prior to such date the participant has withdrawn from the Offering Period as provided in Section 10 hereof.

(c) Merger or Change in Control. In the event of a merger or Change in Control, each outstanding option shall be assumed or an equivalent option substituted by the successor corporation or a Parent or Subsidiary of the successor corporation. In the event that the successor corporation refuses to assume or substitute for the option, the Offering Period then in progress shall be shortened by setting a New Exercise Date and shall end on the New Exercise Date. The New Exercise Date shall be before the date of the Company’s proposed merger or Change in Control. The Administrator shall notify each participant in writing, at least ten (10) business days prior to the New Exercise Date, that the Exercise Date for the participant’s option has been changed to the New Exercise Date and that the participant’s option shall be exercised automatically on the New Exercise Date, unless prior to such date the participant has withdrawn from the Offering Period as provided in Section 10 hereof.

20. Amendment or Termination.

(a) The Administrator may at any time and for any reason terminate or amend the Plan. Except as provided in Section 19 and this Section 20 hereof, no amendment may make any

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change in any option theretofore granted which adversely affects the rights of any participant unless their consent is obtained. To the extent necessary to comply with Section 423 of the Code (or any successor rule or provision or any other applicable law, regulation or stock exchange rule), the Company shall obtain stockholder approval of any amendment in such a manner and to such a degree as required.

(b) Without stockholder approval and without regard to whether any participant rights may be considered to have been “adversely affected,” the Administrator shall be entitled to change the Offering Periods, limit the frequency and/or number of changes in the amount withheld during an Offering Period, establish the exchange ratio applicable to amounts withheld in a currency other than U.S. dollars, permit payroll withholding in excess of the amount designated by a participant in order to adjust for delays or mistakes in the Company’s processing of properly completed withholding elections, establish reasonable waiting and adjustment periods and/or accounting and crediting procedures to ensure that amounts applied toward the purchase of Common Stock for each participant properly correspond with amounts withheld from the participant’s Compensation, and establish such other limitations or procedures as the Administrator determines in its sole discretion advisable which are consistent with the Plan.

(c) Without regard to whether any participant’s rights may be considered to have been “adversely affected”, in the event the Administrator determines that the ongoing operation of the Plan may result in unfavorable financial accounting consequences, the Board may, in its discretion and, to the extent necessary or desirable, modify or amend the Plan to reduce or eliminate such accounting consequence including:

(i) increasing the Purchase Price for any Offering Period including an Offering Period underway at the time of the change in Purchase Price;

(ii) shortening any Offering Period so that Offering Period ends on a new Exercise Date, including an Offering Period underway at the time of the Board action; and

(iii) reducing the number of shares that may be purchased upon exercise of outstanding options.

Such modifications or amendments shall not require stockholder approval or the consent of any Plan participants.

21. Notices. All notices or other communications by a participant to the Company under or in connection with the Plan shall be deemed to have been duly given when received in the form and manner specified by the Company at the location, or by the person, designated by the Company for the receipt thereof.

22. Conditions Upon Issuance of Shares. Shares shall not be issued with respect to an option unless the exercise of such option and the issuance and delivery of such shares pursuant thereto shall comply with all applicable provisions of law, domestic or foreign, including, without limitation, the Securities Act of 1933, as amended, the Exchange Act, the rules and regulations promulgated thereunder, and the requirements of any stock exchange upon which the shares may then be listed, and shall be further subject to the approval of counsel for the Company with respect to such compliance.

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As a condition to the exercise of an option, the Company may require the person exercising such option to represent and warrant at the time of any such exercise that the shares are being purchased only for investment and without any present intention to sell or distribute such shares if, in the opinion of counsel for the Company, such a representation is required by any of the aforementioned applicable provisions of law.

23. Term of Plan. The Plan shall become effective upon the earlier to occur of its adoption by the Board of Directors or its approval by the stockholders of the Company. It shall continue in effect until the later of (i) the date it is terminated under Section 20 hereof or (ii) the date which is ten (10) years after the date such Plan is approved by the Board.

24. Stockholder Approval. The Plan will be subject to approval by the stockholders of the Company within twelve (12) months after the date the Plan is adopted by the Board. Such stockholder approval will be obtained in the manner and to the degree required under Applicable Laws.

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EXHIBIT A

SENORX, INC.

EMPLOYEE STOCK PURCHASE PLAN

SUBSCRIPTION AGREEMENT

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I UNDERSTAND THAT THIS SUBSCRIPTION AGREEMENT SHALL REMAIN IN EFFECT THROUGHOUT SUCCESSIVE OFFERING PERIODS UNLESS TERMINATED BY ME.

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EXHIBIT B

SENORX, INC.

EMPLOYEE STOCK PURCHASE PLAN

NOTICE OF WITHDRAWAL

The undersigned participant in the Offering Period of the SenoRx, Inc. Employee Stock Purchase Plan that began on ____________, ______ (the “Offering Date”) hereby notifies the Company that he or she hereby withdraws from the Offering Period. He or she hereby directs the Company to pay to the undersigned as promptly as practicable all the payroll deductions credited to his or her account with respect to such Offering Period. The undersigned understands and agrees that his or her option for such Offering Period will be automatically terminated. The undersigned understands further that no further payroll deductions will be made for the purchase of shares in the current Offering Period and the undersigned shall be eligible to participate in succeeding Offering Periods only by delivering to the Company a new Subscription Agreement.