Document:

<PAGE>   1
                                                                   EXHIBIT 10.14

                                SECOND AMENDMENT
                     TO 7000 BROADWAY BUILDING OFFICE LEASE
                                    between
                        DENVER JACK LIMITED PARTNERSHIP
                                      and
                ALLOS THERAPEUTICS, INC., A Virginia Corporation
                               Dated June 7, 1996

THIS SECOND AMENDMENT is to that certain office lease (the "Lease") dated
October 30, 1995 and First Amendment to 7000 Broadway Building Office Lease
dated October 30, 1995, by and between Denver Jack Limited Partnership
("Lessor") and Allos Therapeutics, Inc., a Virginia Corporation ("Lessee") with
respect to approximately 4,022 square feet of space on the 3rd floor, known as
Suite 310 (the "Premises"), in the building known as 7000 Broadway, Denver,
Colorado (the "Building"). In the event of any conflict between the terms and
provisions of the Lease as amended by the First Amendment, and the terms and
provisions of this Second Amendment, the terms and provisions of this Second
Amendment shall control.

     1. Amendment to Article 34, Rider Number One of the Lease Document. Lessor
        and Lessee do hereby agree that effective June 12, 1996 (the "Effective
        Date") the description of the Premises shall be deemed to be amended to
        include approximately 2,308 rentable square feet of additional office
        space located on the third (3rd) floor known as Suite 320 (the
        "Expansion Space") as outlined on the diagram of the third (3rd) floor
        of the building, attached hereto as Exhibit "A".

        Tenant's right to occupy and obligation to pay Base Rent on the
        "Expansion Space" shall commence on the "Effective Date" and shall
        terminate with the lease term which is redefined in paragraph 2 of this
        Second Amendment.

        Except as otherwise specifically provided herein, as of the "Effective
        Date" any reference to the term "Premises" in the Lease or any
        amendments thereto, including this Amendment, shall be deemed to include
        the "Expansion Space" as though originally a part of the Premises under
        the Lease and Tenant's occupancy thereof shall be subject to all of the
        terms and conditions of the Lease.

     2. Amendment to Article 1 of the Lease Document. Lessor and Lessee do
        hereby agree that as of the "Effective Date", the lease term as
        described in Article 1 of the Lease shall be extended through June 30,
        2001.

     3. Amendment to Article 35 of Rider Number One to the Lease document. As of
        the "Effective Date", Lessor and Lessee do hereby agree that the Rent
        obligation in Article 35 of Rider Number One to the lease document be
        amended as outlined below:

                  06/12/96 - 12/31/96:    $6,215.16 per month
                  01/01/97 - 12/31/98:    $6,382.75 per month
                  01/01/99 - 06/30/01:    $6,550.33 per month

        Such other charges as may be required by the terms of this Lease to be
        paid by Lessee may be referred to in the Lease document as "Additional
        Rent." Lessor shall have the same rights as to the Additional Rent as it
        has to the payment of the rent set forth above.

        All payments are due on or before the first day of the first full
        calendar month of the term hereof and a like sum on or before the first
        day of each and every successive calendar month thereafter during the
        term hereof. Rent for any period during the term hereof, which is less
        than one month, shall be prorated based on a thirty (30) day calendar
        month. All rents payable hereunder shall be paid to Lessor in lawful
        money of the United States of America constituting legal tender at the
        time of payment, at the office of the building or to such other person
        at such other place as Lessor may, from time to time, designate in
        writing. The current payments or notice to Lessor shall be c/o CB
        Commercial Real Estate Group, Inc., 1050 Seventeenth Street, Suite 800,
        Denver, Colorado 80265.
<PAGE>   2

     4. Tenant Improvements. Lessee shall take the "Expansion Space" in its
        "as-is" condition.

     5. Amendment to Article 39 of Rider Number One to the Lease Document. As of
        the Effective Date, Tenant shall have the right to use on an unassigned,
        unreserved basis, an additional eleven (11) parking spaces in the 7000
        Broadway parking area free of charge the term of the Lease. These spaces
        will be in addition to the twenty (20) parking spaces under Lessee's
        control in the Lease document.

     6. Amendment to Article 38 of Rider Number One of the Lease Document.
        Lessee's percentage of Operating Expenses as of the "Effective Date"
        shall be that proportion which the rentable area leased bears to the
        rentable area of the building. For purposes of the Lease, as herein
        amended, such percentage is 13.94%.

     7. Conflicts. If there is any conflict between the terms and provisions of
        this First Amendment and the terms and provisions of the Lease, the
        terms and provisions of this First Amendment shall govern. Except as
        herein specifically set forth, all other provisions of the Lease shall
        remain in full force and effect and be binding upon the parties in
        accordance with their terms.

LANDLORD:

          DENVER JACK LIMITED PARTNERSHIP
          CB COMMERCIAL REAL ESTATE GROUP, INC.
          AS MANAGER

     By:  /s/ ILLEGIBLE
          -------------------------------------
     Its: Senior Vice President
          -------------------------------------
     By:  /s/ ILLEGIBLE
          -------------------------------------
     Its: Assistant Vice President
          -------------------------------------

TENANT:

          ALLOS THERAPEUTICS,
          A VIRGINIA CORPORATION

     By:  /s/ JOHN T. GREFF
          -------------------------------------
     Its: VP Finance & CFO
          -------------------------------------

STATE OF COLORADO

COUNTY OF ADAMS

The foregoing instrument was acknowledged before me this 17th day of June, 1996
by John T. Guff as VP Finance and CFO.

Witness my hand and official seal.

My commission expires: May 2, 1999

                                             /s/ Lisa D. Lange
                                             -------------------------------
                                             Notary Public

[SEAL]
<PAGE>   3
                                 7000 BROADWAY
                                    BUILDING

                          McDERMOTT PLANNING & DESIGN

                                  EXHIBIT "A"
                                  FLOOR PLAN

                               ALLOS THERAPEUTICS
                             THIRD FLOOR SPACE PLAN<PAGE>   1
                                                                   EXHIBIT 10.15

                                THIRD AMENDMENT
                     TO 7000 BROADWAY BUILDING OFFICE LEASE
                                    between
                    DENVER JACK LIMITED PARTNERSHIP (Lessor)
                                      and
            ALLOS THERAPEUTICS, INC., a Delaware Corporation (Lessee)
                              Dated March 26, 1998

THIS THIRD AMENDMENT is to that certain office lease (the "Lease") dated October
30, 1995, First Amendment to 7000 Broadway Building Office Lease dated October
30, 1995 and Second Amendment to 7000 Broadway Building Office Lease dated June
7, 1996, by and between Denver Jack Limited Partnership ("Lessor") and Allos
Therapeutics, Inc., a Delaware Corporation ("Lessee") with respect to
approximately 4,022 and 2,308 square feet of space on the 3rd floor, known as
Suite 310 and 320 (the "Premises"), in the building known as 7000 Broadway,
Denver, Colorado (the "Building"). In the event of any conflict between the
terms and provisions of the Lease as amended by the First and Second Amendments,
and the terms and provisions of this Third Amendment, the terms and provisions
of this Third Amendment shall control.

     1.   Amendment to Article 34 of Rider Number One to the Lease Document and
          Article 1 of the Second Amendment. Lessor and Lessee do hereby agree
          that effective July 1, 1998 or when Landlord delivers Premises to
          Tenant (the "Effective Date") the description of the Premises shall be
          deemed to be amended to include approximately 9,208 rentable square
          feet of office space located on the fourth (4th) floor known as Suite
          400 (the "New Premises") as outlined on the diagram of the fourth
          (4th) floor of the building, attached hereto as Exhibit "A".

          As of the Effective Date, Lessee shall be released of its obligation
          from suite 310 excluding the shower area consisting of approximately
          3,810 rentable square feet leaving approximately 2,520 rentable square
          feet in suite 320 and shower area ("suite 320").

          Lessee's right to occupy and obligation to pay Base Rent on the "New
          Premises" shall commence on the "Effective Date" and shall terminate
          with the lease term which is redefined in paragraph 2 of this Third
          Amendment.

          Except as otherwise specifically provided herein, as of the "Effective
          Date" any reference to the term "Premises" and/or "New Premises" in
          the Lease or any amendments thereto, including this Amendment, shall
          be known as suite 400, approximately 9,208 rentable square feet and
          suite 320, approximately 2,520 rentable square feet and Lessee's
          occupancy thereof shall be subject to all of the terms and conditions
          of the Lease.

     2.   Amendment to Article 1 of the Lease Document and Article 2 of the
          Second Amendment. Lessor and Lessee do hereby agree that as of the
          "Effective Date", the lease term as described in Article 1 of the
          Lease and Article 2 of the Second Amendment shall remain the same for
          suite 320 and shall be extended through April 30, 2002 for suite 400.

     3.   Amendment to Article 35 of Rider Number One to the Lease document and
          Article 3 of the Second Amendment. As of the "Effective Date", Lessor
          and Lessee do hereby agree that the Rent obligation in Article 35 of
          Rider Number One and Article 3 of the Second Amendment to the lease
          document be amended as outlined below:

               Suite 400 Approximately 9,208 Rentable Square Feet
               --------------------------------------------------

<TABLE>
<S>                           <C>                           <C>
07/01/98 - 06/30/99           $10,359.00 per month          ($13.50 RSF/Yr)
07/01/99 - 06/30/00           $10,550.83 per month          ($13.75/RSF/Yr)
07/01/00 - 06/30/01           $10,934.50 per month          ($14.25/RSF/Yr)
07/01/01 - 06/30/02           $11,126.33 per month          ($14.50 RSF/Yr)
</TABLE>

               Suite 320 Approximately 2,520 Rentable Square Feet
               --------------------------------------------------

<TABLE>
<S>                           <C>                           <C>
07/01/98 - 12/31/98           $2,541.00 per month           ($12.10/RSF/Yr)
01/01/99 - 06/30/01           $2,608.20 per month           ($12.42/RSF/Yr)
</TABLE>

<PAGE>   2
          Such other charges as may be required by the terms of this Lease to be
          paid by Lessee may be referred to in the Lease document as "Additional
          Rent." Lessor shall have the same rights as to the Additional Rent as
          it has to the payment of the rent set forth above.

          All payments are due on or before the first day of the first full
          calendar month of the term hereof and a like sum on or before the
          first day of each and every successive calendar month thereafter
          during the term hereof. Rent for any period during the term hereof,
          which is less than one month, shall be prorated based on a thirty (30)
          day calendar month. All rents payable hereunder shall be paid to
          Lessor in lawful money of the United States of America constituting
          legal tender at the time of payment, at the office of the building or
          to such other person at such other place as Lessor may, from time to
          time, designate in writing. The current payments or notice to Lessor
          shall be c/o CB Commercial Real Estate Group, Inc., 1050 Seventeenth
          Street, Suite 800, Denver, Colorado 80265.

     4.   Lessee Improvements. Lessor shall provide "turnkey" Lessee
          improvements with building standard materials per the attached Exhibit
          "A" prepared by McDermott Planning dated March 26, 1998. Any increase
          in cost of the Lessee improvements due to Lessee changing, modifying
          or altering the plan shall be the responsibility of Lessee.

     5.   Amendment to Article 39 of Rider Number One to the Lease Document and
          Article 5 of the Second Amendment. As of the Effective Date, Lessee
          shall have the right to use on an unassigned, unreserved basis, one
          (1) parking space for every 200 rentable square feet leased in the
          7000 Broadway parking area free of charge for the term of the Lease.

     6.   Amendment to Article 38 of Rider Number One of the Lease Document and
          Article 6 of the Second Amendment. Lessee's percentage of Operating
          Expenses as of the "Effective Date" shall be 5.54% for suite 320 and
          20.27% for suite 400.

     7.   Moving Allowance. Lessor shall provide Lessee with up to $18,416.00 to
          offset costs associated with moving of furniture, equipment,
          telecommunications and data communications lines, and changing of
          letterhead. Said allowance shall be paid to Lessee upon Lessee's
          furnishing original receipts of each expense to Lessor.

     8.   Conflicts. If there is any conflict between the terms and provisions
          of this Third Amendment and the terms and provisions of the Lease as
          amended by the First and Second Amendments, the terms and provisions
          of this Third Amendment shall govern. Except as herein specifically
          set forth, all other provisions of the Lease shall remain in full
          force and effect and be binding upon the parties in accordance with
          their terms.

LESSOR:                                      LESSEE:

AMBERJACK, LTD., GENERAL PARTNER FOR         ALLOS THERAPEUTICS
DENVER JACK LIMITED PARTNERSHIP BY           A DELAWARE CORPORATION
CB COMMERCIAL REAL ESTATE GROUP,  INC.,
AS MANAGER

By:  /s/  [ILLEGIBLE]                        By:  /s/  Stephen J. Hoffman
     ---------------------------------            -----------------------------

Its:   Vice President                        Its:   CEO
     ---------------------------------            -----------------------------

By:  /s/  [ILLEGIBLE]                        By:
     ---------------------------------            -----------------------------

Its:   SVP                                   Its:
     ---------------------------------            -----------------------------

STATE OF COLORADO

COUNTY OF ADAMS

The foregoing instrument was acknowledge before me this 7th day of
April, 1998 by Stephen J. Hoffman as CEO.

Witness my hand and official seal.

My commission expires: 5/2/99

                                       /s/     LISA D. LANGE
                                       -------------------------------
                                       Notary Public
(SEAL)
<PAGE>   3
                                 CB COMMERCIAL

                                 [EXHIBIT "A"]

                                ALLOS SPACE PLAN

NOT TO SCALE                                                [NORTH LOGO]
<PAGE>   4
                                  [FLOOR PLAN]

                                 [EXHIBIT "B"]

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