THIRD LEASE AMENDMENT TO OFFICE LEASE (LEASE EXTENSION)

Exhibit 10.5

THIRD LEASE AMENDMENT

(LEASE EXTENSION)

This Third Lease Amendment is to the Office Building Lease and Addendum One and Addendum Two dated May 18, 1999 (the “Lease”), by and between Lake Union Building, LLC (“Landlord”), and Insightful Corporation, formerly known as Mathsoft, Inc. (“Tenant”). To the extent the terms of this Amendment are inconsistent with the other terms of the Lease, the terms of this Amendment shall control. Unless specifically stated otherwise, all capitalized terms in this Amendment shall have the same meaning ascribed to them in the Lease.

1. PREMISES

That portion of the Building containing the following:

(a) Approximately 960 square feet of Rentable Area located on the first (1st) floor of the Building and consisting of the space known as Suite 120;

(b) Approximately 8,247 square feet of Rentable Area located on the fourth (4th) floor of the Building and consisting of the space known as Suite 400;

(c) Approximately 12,654 square feet of Rentable Area located on the fifth (5th) floor of the Building;

(d) Approximately 3,530 square feet of Rentable Area located on the sixth (6th) floor of the Building and consisting of the space known as Suite 610.

All Rentable Area measurements are calculated in accordance with the BOMA Standard Method for Measuring Floor Area in Office Buildings (ANSI/BOMA Z65.1-1996).

2. EXPANSION SPACE (SUITE 410)

The Premises shall be expanded hereby to include approximately 1,979 square feet of Rentable Area located on the fourth (4th) floor of the Building and consisting of the space known as Suite 410 (the “Expansion Space”).

3. FINAL RENTABLE AREA – FLOOR 4

The final Rentable Area of Tenant’s Premises on Floor 4 shall be subject to the final configuration of the Expansion Space as determined by a mutually acceptable space plan. In the event the Rentable Area of Tenant’s Premises on Floor 4 shall change as the result of such space plan, Landlord shall prepare an amendment to the Lease revising Tenant’s Premises, Rentable Area and Rent; Tenant and Landlord shall promptly execute the amendment.

4. LEASE TERM EXTENSION

The Landlord and Tenant hereby agree to extend the term of the Lease for an additional extension term of thirty-six months, commencing October 1, 2007, and ending September 30, 2010 (the “Lease Term Extension”).

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June 8, 2007

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5. COMMENCEMENT OF LEASE TERM EXTENSION

October 1, 2007

6. EXPIRATION OF LEASE TERM EXTENSION

September 30, 2010

7. COMMENCEMENT OF RENT – EXPANSION SPACE (SUITE 410)

Tenant shall commence payment of Rent for the Expansion Space upon the completion or substantial completion of construction of improvements to the Expansion Space; however, in no case shall payment of Rent by Tenant for the Expansion Space commence later than May 1, 2008.

8. RENTAL RATE – LEASE TERM EXTENSION PERIOD

The rental rates during the Lease Term Extension shall be the fully serviced rates charged Tenant by Landlord per Rentable Square Foot (RSF) as set forth below:

The rental rates shall be as follows:

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9. PARKING

Prior to completion of Landlord’s repairs to the parking garage structure at The Lake Union Building, Tenant shall have an option for parking at a rate of one (1) parking space per one thousand (1,000) feet of Rentable Area leased. Following completion of Landlord’s repairs to the parking garage structure at The Lake Union Building, Tenant shall have an option for parking at a rate of two (2) parking spaces per one thousand (1,000) feet of Rentable Area leased. All parking arrangements shall be made through Landlord’s parking lot contractor, Ampco System Parking (206-267-0710). The location of allocated parking shall be subject to availability.

If at the commencement of the Lease Term Extension Tenant elects not to rent parking spaces allotted to it or if during the Lease Term Extension any of Tenant’s parking spaces are returned to Landlord, reassignment of such parking spaces shall be subject to availability and may be on a month-to-month basis only.

Additional parking spaces, if any, may be made available to Tenant on a month-to-month basis. Landlord reserves the right to reclaim such month-to-month parking spaces from Tenant upon thirty (30) days advance written notice to Tenant by Landlord.

Parking rates are determined by market conditions and are subject to change. The parking rates charged as of June 8, 2007 are:

10. OPTION TO RENEW

Landlord hereby grants to Tenant one option (the “Option”) to extend the Lease Term for an additional term of three (3) years (the “Extension Term”).

All terms and conditions of the Lease shall apply to the Extension Term except that Base Rent during the Extension Term shall be an amount equal to the greater of: (a) the Base Rent payable immediately prior to the Extension Term; or (b) the then annual Market Rent. “Market Rent” shall be the annual Base Rent payable for each year of the Extension Term (calculated on a per rentable square foot basis), commencing on the first day of the Extension Term for comparable office space in the Lake Union area, taking into consideration the normal concessions available to

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tenants in the market. Landlord and Tenant shall have one (1) month after Landlord receives the extension notice from Tenant in which to agree on Market Rent. If the parties are unable to agree on Market Rent within that period, then Market Rent shall be determined by binding arbitration conducted in accordance with the applicable rules of the American Arbitration Association and procedures set forth in RCW 7.04 then in effect; provided there shall be only one arbitrator. The method of arbitration shall be that known as the “baseball” type of arbitration: Each party shall submit to the arbitrator and exchange with each other in advance of the hearing their last, best offers as to the Market Rent. The arbitrator shall be limited to awarding only one or the other of the two figures submitted. The Market Rent established by the arbitrator shall be determined no later than sixty (60) days prior to the start of the Extension Term and shall be binding on the parties. Each party shall pay the cost of its experts and attorneys. The arbitrator must have a minimum of five (5) years’ prior experience in the commercial leasing market in Seattle, King County, Washington. The costs and expenses of the arbitrator shall be divided equally between Landlord and Tenant.

The Option shall be exercised only by written notice delivered to Landlord at least one hundred eighty (180) days before the expiration of the Lease Term. If Tenant fails to deliver Landlord written notice of the exercise of an Option within the prescribed time period, such Option shall lapse, and there shall be no further right to extend the Lease Term. The Option shall be exercisable by Tenant on the express conditions that (a) at the time of the exercise, and at all times prior to the commencement of such Extension, Tenant shall not be in default under any of the provisions of this Lease and (b) Tenant shall not have committed an Event of Default, and (c) Tenant has not been ten (10) or more days late in the payment of rent more than a total of three (3) times during the Lease Term.

11. TENANT IMPROVEMENTS

Landlord shall provide Tenant the following tenant improvement allowances:

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Landlord shall permit Tenant to combine the total of all tenant improvement allowances provided herein (the “Tenant Improvement Allowance”), and Tenant may use the proceeds of the Tenant Improvement Allowance to improve any portion of the Premises as provided for herein and pursuant to Exhibit A (Workletter).

The Tenant Improvement Allowance shall be used only for space planning or construction of improvements including, but not limited to, b