<PAGE>

                                                                     Exhibit 4.2

THE SECURITIES EVIDENCED BY THIS WARRANT HAVE NOT BEEN REGISTERED UNDER THE
SECURITIES ACT OF 1933, AS AMENDED, OR APPLICABLE STATE SECURITIES LAWS, AND NO
INTEREST MAY BE SOLD, DISTRIBUTED, ASSIGNED, OFFERED, PLEDGED OR OTHERWISE
TRANSFERRED UNLESS (A) THERE IS AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH
ACT AND APPLICABLE STATE SECURITIES LAWS COVERING ANY SUCH TRANSACTION INVOLVING
SAID SECURITIES, (B) THE COMPANY RECEIVES AN OPINION OF LEGAL COUNSEL FOR THE
HOLDER OF THE SECURITIES SATISFACTORY TO THE COMPANY STATING THAT SUCH
TRANSACTION IS EXEMPT FROM REGISTRATION OR (C) THE COMPANY OTHERWISE SATISFIES
ITSELF THAT SUCH TRANSACTION IS EXEMPT FROM REGISTRATION.

No. W-___                                       WARRANT TO PURCHASE COMMON STOCK
ISSUED:  __________, 2005
Void After _________, 2015

                          LIGHT SCIENCES ONCOLOGY, INC.

                                     WARRANT

     THIS IS TO CERTIFY that, for value received and subject to these terms and
conditions, _______________, or such person to whom this Warrant is transferred
(the "HOLDER"), is entitled to exercise this Warrant to purchase ________ fully
paid and nonassessable shares of Light Sciences Oncology, Inc., a Washington
corporation (the "COMPANY"), $0.001 par value per share of common stock (the
"WARRANT STOCK") at a price per share of [$6.25] (the "EXERCISE PRICE") (such
number of shares, type of security and the Exercise Price being subject to
adjustment as provided below).

1.   METHOD OF EXERCISE

     1.1  CASH EXERCISE RIGHT

     This Warrant may be exercised by the Holder, at any time after the date of
issuance, but not later than _____________, 2015 (the "EXERCISE PERIOD"), in
whole or in part, by delivering to the Company at 34931 SE Douglas Street, Suite
200, Snoqualmie, WA 98065 (or such other office or agency of the Company as it
may designate by notice in writing to the Holder at the address of the Holder
appearing on the books of the Company) (a) this Warrant certificate, (b) a
certified or cashier's check payable to the Company, or canceled indebtedness of
the Company to the Holder, in the amount of the Exercise Price multiplied by the
number of shares for which this Warrant is being exercised (the "PURCHASE
PRICE"), and (c) the Notice of Cash Exercise attached as EXHIBIT A duly
completed and executed by the Holder. Upon exercise, the Holder shall be
entitled to receive from the Company a stock certificate in proper form
representing the number of shares of Warrant Stock purchased.


                                      -1-

<PAGE>

     1.2  NET ISSUANCE RIGHT

     Notwithstanding the payment provisions set forth above, the Holder may
elect to convert all or a portion of this Warrant into shares of Warrant Stock
by surrendering this Warrant at the office of the Company at the address set
forth in Section 1.1 and delivering to the Company the Notice of Net Issuance
Exercise attached as EXHIBIT B duly completed and executed by the Holder, in
which case the Company shall issue to the Holder the number of shares of Warrant
Stock of the Company equal to the result obtained by (a) subtracting B from A,
(b) multiplying the difference by C, and (c) dividing the product by A as set
forth in the following equation:

                             X = (A - B) x C where:
                                      A

X    = the number of shares of Warrant Stock issuable upon net issuance exercise
       pursuant to the provisions of this Section 1.2.

A    = the Fair Market Value (as defined below) of one share of Warrant Stock on
       the date of net issuance exercise.

B    = the Exercise Price for one share of Warrant Stock under this Warrant (as
       adjusted from time to time pursuant to Section 4 hereof).

C    = the number of shares of Warrant Stock as to which this Warrant is
       exercisable pursuant to the provisions of this Warrant or, if only a
       portion of this Warrant is being exercised, the portion of this Warrant
       being exercised as set forth in the Notice of Net Issuance Exercise.

     If the foregoing calculation results in a negative number, then no shares
of Warrant Stock shall be issued upon net issuance exercise pursuant to this
Section 1.2.

     "FAIR MARKET VALUE" of a share of Warrant Stock shall mean:

     (a) if the net issuance exercise is in connection with a transaction
specified in Section 4.1, the value of the consideration (determined, in the
case of noncash consideration, in good faith by the Company's Board of
Directors) to be received pursuant to such transaction by the holder of one
share of Warrant Stock;

     (b) if the net issuance exercise is in connection with the initial public
offering of the Company's common stock, $0.001 par value per share (the "COMMON
STOCK"), the initial public offering price (before deducting commission,
discounts or expenses) at which the Common Stock is sold in such offering;


                                      -2-

<PAGE>

     (c) if the net issuance exercise is after the occurrence of the initial
public offering of the Company's Common Stock:

          (1) if the Company's Common Stock is traded on an exchange or is
quoted on the Nasdaq National Market, the average of the closing or last sale
price reported for the 5 trading days immediately preceding the date of net
issuance exercise;

          (2) if the Company's Common Stock is not traded on an exchange or on
the Nasdaq National Market, but is traded in the over-the-counter market, the
average of the closing bid and asked prices reported for the 5 trading days
immediately preceding the date of net issuance exercise; and

     (d) In all other cases, the fair value as determined in good faith by the
Company's Board of Directors.

     Upon net issuance exercise in accordance with this Section 1.2, the Holder
shall be entitled to receive from the Company a stock certificate in proper form
representing the number of shares of Warrant Stock determined in accordance with
the foregoing.

2.   DELIVERY OF STOCK CERTIFICATES; NO FRACTIONAL SHARES

     (a) Within 10 days after the payment of the Purchase Price following the
exercise of this Warrant (in whole or in part) or after notice of net issuance
exercise and compliance with Section 1.2, the Company at its expense shall issue
in the name of and deliver to the Holder (i) a certificate or certificates for
the number of fully paid and nonassessable shares of Warrant Stock to which the
Holder shall be entitled upon such exercise, and (ii) a new Warrant of like
tenor to purchase up to that number of shares of Warrant Stock, if any, as to
which this Warrant has not been exercised if this Warrant has not expired. The
Holder shall for all purposes be deemed to have become the holder of record of
such shares of Warrant Stock on the date this Warrant was exercised (the date
the Holder has fully complied with the requirements of Section 1.1 or 1.2),
irrespective of the date of delivery of the certificate or certificates
representing the Warrant Stock; provided that, if the date such exercise is made
is a date when the stock transfer books of the Company are closed, such person
shall be deemed to have become the holder of record of such shares of Warrant
Stock at the close of business on the next succeeding date on which the stock
transfer books are open.

     (b) No fractional shares shall be issued upon the exercise of this Warrant.
In lieu of fractional shares, the Company shall pay the Holder a sum in cash
equal to such fraction multiplied by the Exercise Price.

3.   COVENANTS AS TO WARRANT STOCK; REPRESENTATIONS OF THE COMPANY

     (a) The Company covenants that at all times during the Exercise Period
there shall be reserved for issuance and delivery upon exercise of this Warrant
such number of shares of Warrant Stock as is necessary for exercise in full of
this Warrant and, from time to time, it will take all steps necessary to amend
its Articles of Incorporation to provide


                                      -3-

<PAGE>

sufficient reserves of shares of Warrant Stock. All shares of Warrant Stock
issued pursuant to the exercise of this Warrant will, upon their issuance, be
validly issued and outstanding, fully paid and nonassessable, free and clear of
all liens and other encumbrances or restrictions on sale and free and clear of
all preemptive rights, except restrictions arising (i) under federal and state
securities laws, (ii) not by or through the Company, or (iii) by agreement
between the Company and the Holder or its successors.

     (b) The Company hereby represents and warrants to the Holder as of the date
of this Warrant: (i) the Company is a corporation duly incorporated and validly
existing under the laws of the State of Washington; (ii) the Company has full
power and authority to execute and deliver this Warrant and to perform its
obligations under and consummate the transactions contemplated by this Warrant;
(iii) upon the execution of this Warrant by the Company and delivery of this
Warrant, this Warrant shall have been duly and validly executed and delivered by
the Company and shall constitute the legal, valid and binding obligation of the
Company, enforceable against the Company in accordance with its terms; and (iv)
the Warrant Stock, if issued, will be, duly authorized, validly issued, fully
paid and nonassessable shares of the capital stock of the Company.

4.   ADJUSTMENTS; TERMINATION OF WARRANT UPON CERTAIN EVENTS

     4.1  EFFECT OF REORGANIZATION

          (A)  REORGANIZATION--NO CHANGE IN CONTROL

          Upon a merger, consolidation, share exchange, acquisition of all or
substantially all of the property or stock, liquidation or other reorganization
of the Company (collectively, a "REORGANIZATION") during the Exercise Period, as
a result of which the shareholders of the Company receive cash, stock or other
property in exchange for their shares of Warrant Stock and the holders of the
Company's voting equity securities immediately prior to such Reorganization
together own a majority interest of the voting equity securities of the
successor corporation following such Reorganization, lawful provision shall be
made so that the Holder shall thereafter be entitled to receive, upon exercise
of this Warrant, the number of shares of securities of the successor corporation
resulting from such Reorganization (and cash and other property), to which a
holder of the Warrant Stock issuable upon exercise of this Warrant would have
been entitled in such Reorganization if this Warrant had been exercised
immediately prior to such Reorganization. In any such case, appropriate
adjustment (as determined in good faith by the Company's Board of Directors)
shall be made in the application of the provisions of this Warrant with respect
to the rights and interest of the Holder after the Reorganization to the end
that the provisions of this Warrant (including adjustments of the Exercise Price
and the number and type of securities purchasable pursuant to the terms of this
Warrant) shall be applicable after that event, as near as reasonably may be, in
relation to any shares deliverable after that event upon the exercise of this
Warrant.


                                      -4-

<PAGE>

          (B)  REORGANIZATION--CHANGE IN CONTROL; TERMINATION OF WARRANT

          If a Reorganization, as a result of which the shareholders of the
Company receive cash, stock or other property in exchange for their shares of
Warrant Stock and the holders of the Company's voting equity securities
immediately prior to such Reorganization together do not own at least majority
interest of the voting equity securities of the successor corporation (or its
parent) following such Reorganization, is to be effected during the Exercise
Period, the Company shall give the Holder written notice of such proposed
Reorganization at least 10 days before the effectiveness of such proposed
Reorganization. Notwithstanding the period of exercisability stated on the face
of this Warrant, this Warrant shall expire upon the closing of such
Reorganization.

     4.2  ADJUSTMENTS FOR STOCK SPLITS, DIVIDENDS, RECLASSIFICATION, ETC.

     If the Company shall issue any shares of the same class as the securities
for which this Warrant is exercisable as a stock dividend or subdivide the
number of outstanding shares of such class into a greater number of shares,
then, in either such case, the Exercise Price in effect before such dividend or
subdivision shall be proportionately reduced and the number of shares of Warrant
Stock at that time issuable pursuant to the exercise of this Warrant shall be
proportionately increased; and, conversely, if the Company shall contract the
number of outstanding shares of the same class as the securities for which this
Warrant is exercisable by combining such shares into a smaller number of shares,
then the Exercise Price in effect before such combination shall be
proportionately increased and the number of shares of Warrant Stock at that time
issuable pursuant to the exercise or conversion of this Warrant shall be
proportionately decreased. If the Company at any time while this Warrant, or any
portion thereof, remains outstanding and unexpired shall, by reclassification of
securities or otherwise, change any of the securities as to which purchase
rights under this Warrant exist into the same or a different number of
securities of any other class or classes, this Warrant shall thereafter
represent the right to acquire such number and kind of securities as would have
been issuable as the result of such change with respect to the securities which
were subject to the purchase rights under this Warrant immediately prior to such
reclassification or other change and the Exercise Price therefor shall be
appropriately adjusted all subject to further adjustments as provided in Section
4. Each adjustment in the number of shares of Warrant Stock issuable shall be to
the nearest whole share.

     4.3  CERTIFICATE AS TO ADJUSTMENTS

     In the case of any adjustment in the Exercise Price or number and type of
securities issuable upon exercise of this Warrant, the Company will promptly
give written notice to the Holder in the form of a certificate, certified and
confirmed by an officer of the Company, setting forth the adjustment in
reasonable detail.


                                      -5-

<PAGE>

5.   SECURITIES LAWS RESTRICTIONS; LEGEND ON WARRANT STOCK

     (a) This Warrant and the securities issuable upon exercise have not been
registered under the Securities Act of 1933, as amended (the "SECURITIES ACT"),
or applicable state securities laws, and no interest may be sold, distributed,
assigned, offered, pledged or otherwise transferred unless (i) there is an
effective registration statement under such Securities Act and applicable state
securities laws covering any such transaction involving said securities, (ii)
the Company receives an opinion of legal counsel for the holder of the
securities satisfactory to the Company stating that such transaction is exempt
from registration, or (iii) the Company otherwise satisfies itself that such
transaction is exempt from registration.

     (b) The legends set forth below shall be placed on this Warrant, any
replacement and any certificate representing the Warrant Stock, and a stop
transfer order shall be placed on the books of the Company and with any transfer
agent until such securities may be legally sold or otherwise transferred:

          THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR
          INVESTMENT AND NOT WITH A VIEW TO, OR IN CONNECTION WITH, THE SALE OR
          DISTRIBUTION THEREOF, AND HAVE NOT BEEN REGISTERED UNDER THE
          SECURITIES ACT OF 1933, AS AMENDED, OR APPLICABLE STATE SECURITIES
          LAWS, AND NO INTEREST MAY BE SOLD, DISTRIBUTED, ASSIGNED, OFFERED,
          PLEDGED OR OTHERWISE TRANSFERRED UNLESS (A) THERE IS AN EFFECTIVE
          REGISTRATION STATEMENT UNDER SUCH ACT AND APPLICABLE STATE SECURITIES
          LAWS COVERING ANY SUCH TRANSACTION INVOLVING SAID SECURITIES, (B) THE
          COMPANY RECEIVES AN OPINION OF LEGAL COUNSEL FOR THE HOLDER OF THE
          SECURITIES SATISFACTORY TO THE COMPANY STATING THAT SUCH TRANSACTION
          IS EXEMPT FROM REGISTRATION OR (C) THE COMPANY OTHERWISE SATISFIES
          ITSELF THAT SUCH TRANSACTION IS EXEMPT FROM REGISTRATION.

          THE SHARES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO RESTRICTIONS
          ON TRANSFERABILITY AND RESALE, INCLUDING A LOCK UP PERIOD IN THE EVENT
          OF A PUBLIC OFFERING, AS SET FORTH IN A STOCK PURCHASE WARRANT, A COPY
          OF WHICH MAY BE OBTAINED AT THE PRINCIPAL OFFICE OF THE COMPANY. SUCH
          RESTRICTIONS ARE BINDING ON TRANSFEREES OF THESE SHARES.


                                      -6-

<PAGE>

6.   EXCHANGE OF WARRANT; LOST OR DAMAGED WARRANT CERTIFICATE

     This Warrant is exchangeable upon its surrender by the Holder at the office
of the Company. Upon receipt by the Company of satisfactory evidence of the
loss, theft, destruction or damage of this Warrant and either (in the case of
loss, theft or destruction) delivery of an indemnity agreement reasonably
satisfactory in form and substance to the Company or (in the case of damage) the
surrender of this Warrant for cancellation, the Company will execute and deliver
to the Holder, without charge, a new Warrant of like denomination.

7.   REPRESENTATIONS AND WARRANTIES BY THE HOLDER

     By accepting this Warrant, the Holder represents and warrants to the
Company as follows:

     (a) This Warrant and the securities issuable upon exercise thereof are
being acquired for its own account, for investment and not with a view to, or
for resale in connection with, any distribution or public offering thereof
within the meaning of the Securities Act. Upon exercise of this Warrant, the
Holder shall, if so requested by the Company, confirm in writing, in a form
satisfactory to the Company, that the securities issuable upon exercise of this
Warrant are being acquired for investment and not with a view toward
distribution or resale.

     (b) The Holder understands that the Warrant and the securities issuable
upon exercise have not been registered under the Securities Act by reason of
their issuance in a transaction exempt from the registration and prospectus
delivery requirements of the Securities Act pursuant to Section 4(2) thereof,
and that they must be held by the Holder indefinitely, and that the Holder must
therefore bear the economic risk of such investment indefinitely, unless a
subsequent disposition thereof is registered under the Securities Act or is
exempted from such registration.

     (c) The Holder has such knowledge and experience in financial and business
matters that it is capable of evaluating the merits and risks of the purchase of
this Warrant and the securities purchasable pursuant to the terms of this
Warrant and of protecting its interests in connection therewith.

     (d) The Holder is able to bear the economic risk of the purchase of the
securities issuable upon exercise of this Warrant pursuant to the terms of this
Warrant.

     (e) The Holder is an "accredited investor" as such term is defined in Rule
501 of Regulation D promulgated under the Securities Act.

     (f) The Holder acknowledges that the Company has made no representation
regarding the potential or actual tax consequences for the Holder which will
result from the issuance of this Warrant. The Holder acknowledges that the
Holder bears complete responsibility for obtaining adequate tax advice regarding
this Warrant.


                                      -7-

<PAGE>

8.   MISCELLANEOUS

     8.1  HOLDER AS OWNER

     The Company may deem and treat the holder of record of this Warrant as the
absolute owner for all purposes regardless of any notice to the contrary.

     8.2  NO SHAREHOLDER RIGHTS

     This Warrant shall not entitle the Holder to any voting rights (whether for
the election of directors or otherwise), to give or withhold consent to any
corporate action (whether upon any recapitalization, issuance of stock,
reissuance of stock, change of par value, consolidation, merger, conveyance or
otherwise), to receive notice of meetings or to any other rights as a
shareholder of the Company or to any other rights except the rights stated
herein; and no dividend or interest shall be payable or shall accrue in respect
of this Warrant or the Warrant Stock, until this Warrant is exercised and the
securities purchasable upon the exercise hereof shall have become deliverable,
as provided herein.

     8.3  NOTICES

     Unless otherwise provided, any notice under this Warrant shall be given in
writing and shall be deemed effectively given (a) upon personal delivery to the
party to be notified, (b) upon confirmation of receipt by fax by the party to be
notified, (c) one business day after deposit with a reputable overnight courier,
prepaid for overnight delivery and addressed as set forth in (d), or (d) three
days after deposit with the United States Post Office, postage prepaid,
registered or certified with return receipt requested and addressed to the party
to be notified at the address indicated below, or at such other address as such
party may designate by 10 days' advance written notice to the other party given
in the foregoing manner.

     If to the Holder: To the address and facsimile number last furnished in
writing to the Company by the Holder.

     If to the Company:

     Light Sciences Oncology, Inc.
     34931 SE Douglas Street, Suite 200
     Snoqualmie, WA 98065
     Fax: (425) 392-7392

     8.4  AMENDMENTS AND WAIVERS

     Any term of this Warrant may be amended and the observance of any term may
be waived (either generally or in a particular instance and either retroactively
or prospectively) only with the written consent of the Company and the Holder.
Any amendment or waiver


                                      -8-

<PAGE>

effected in accordance with this Section 8.4 shall be binding on each future
Holder and the Company.

     8.5  GOVERNING LAW; JURISDICTION; VENUE

     This Warrant shall be governed by and construed under the laws of the State
of Washington without regard to principles of conflict of laws. The parties
irrevocably consent to the jurisdiction and venue of the state and federal
courts located in King County, Washington in connection with any action relating
to this Warrant.

     8.6  SUCCESSORS AND ASSIGNS; TRANSFER

     The terms and conditions of this Warrant shall inure to the benefit of and
be binding on the respective successors and assigns of the parties. This Warrant
may not be transferred or assigned without the consent of the Company, except to
a partner, member or shareholder of the Holder provided that such partner,
member or shareholder agrees in writing to assume the obligations of a "Holder"
set forth herein.

     8.7  "MARKET STAND OFF" AGREEMENT

     In connection with any underwritten public offering by the Company of its
equity securities pursuant to an effective registration statement filed under
the Securities Act, including the Company's initial public offering, the Holder
hereby agrees that the Holder shall not sell or otherwise transfer or dispose of
any of the Company's securities held by the Holder (other than those included in
the registration at issue, if any) for a period specified by the representative
of the underwriters of Common Stock of the Company not to exceed (i) one hundred
eighty (180) days following the effective date of the registration statement for
such initial public offering or (ii) such longer period requested by the
underwriters as is necessary to comply with regulatory restrictions on the
publication of research reports (including, but not limited to, NASD Rule 2711);
provided, however, that the Holder shall not be subject to such lockup unless
the officers and directors of the Company who own stock of the Company and all
other persons or entities who own beneficially at least 5% of the Common Stock
within the meaning of Rule 13d-3 under the Securities Exchange Act of 1934, as
amended) are also be bound by such restrictions. The Holder agrees to execute
and deliver such other agreements as may be reasonably requested by the Company
or the underwriter which are consistent with the foregoing or which are
necessary to give further effect thereto. The Company may impose stop transfer
instructions with respect to the shares of Common Stock (or other securities)
subject to the foregoing restriction until the end of said period.

                                      * * *


                                      -9-

<PAGE>

     IN WITNESS WHEREOF, the parties have executed this Warrant as of the date
first written above.

                                        LIGHT SCIENCES ONCOLOGY, INC.


                                        By:
                                            ------------------------------------
                                            Llew Keltner, President


 ------------------------


By:
    ---------------------------------
Its:
     --------------------------------
<PAGE>

                                    EXHIBIT A

                             NOTICE OF CASH EXERCISE

To : Light Sciences Oncology, Inc.

     The undersigned hereby irrevocably elects to purchase ________ shares of
Common Stock of Light Sciences Oncology, Inc. (the "COMPANY") issuable upon the
exercise of the attached Warrant and requests that certificates for such shares
be issued in the name of and delivered to the address of the undersigned, at the
address stated below and, if said number of shares shall not be all the shares
that may be purchased pursuant to the attached Warrant, that a new Warrant
evidencing the right to purchase the balance of such shares be registered in the
name of, and delivered to, the undersigned at the address stated below. The
undersigned agrees with and represents to the Company that said shares of the
Common Stock of the Company are acquired for the account of the undersigned for
investment and not with a view to, or for sale in connection with, any
distribution or public offering within the meaning of the Securities Act of
1933, as amended (the "SECURITIES ACT"). In addition, the undersigned represents
that he, she or it (as the case may be) is an "accredited investor" as such term
is defined in Rule 501(a) of the Securities Act.

Payment enclosed in the amount of $                    .
                                    -------------------

Dated:
       -------------------

Name of Holder of Warrant:
                           -----------------------------------------------------
                                               (please print)
Address:
         -----------------------------------------------------------------------

         -----------------------------------------------------------------------

         -----------------------------------------------------------------------


Signature:
           ---------------------------------------------------------------------

RECEIVED with full payment on                  , 20  .
                              -----------------    --


By:
    ---------------------------------

Print name:                          , on behalf of the Company
            -------------------------
<PAGE>

                                    EXHIBIT B

                         NOTICE OF NET ISSUANCE EXERCISE

To: Light Sciences Oncology, Inc.

     The undersigned hereby irrevocably elects to convert that amount of the
attached Warrant as specified below into such number of shares of Common Stock
of Light Sciences Oncology, Inc. (the "COMPANY") as is determined pursuant to
Section 1.2 of the attached Warrant. The undersigned requests that certificates
for such net issuance shares be issued in the name of and delivered to the
address of the undersigned, at the address stated below. The undersigned agrees
with and represents to the Company that said shares are acquired for the account
of the undersigned for investment and not with a view to, or for sale in
connection with, any distribution or public offering within the meaning of the
Securities Act of 1933, as amended (the "SECURITIES Act"). In addition, the
undersigned represents that he, she or it (as the case may be) is an "accredited
investor" as such term is defined in Rule 501(a) of the Securities Act.

Dated:
       ------------------
Name of Holder of Warrant:
                           -----------------------------------------------------
                                              (please print)


Number of Shares to be Converted:
                                  ----------------------------------------------
Address:
         -----------------------------------------------------------------------

         -----------------------------------------------------------------------

         -----------------------------------------------------------------------


Signature:
           ---------------------------------------------------------------------