AGREEMENT TO PAY MILESTONE PAYMENT

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Exhibit 10.12(b)

Confidential Materials omitted and filed separately with the
Securities and Exchange Commission. Asterisks denote omissions.

Millennium Pharmaceuticals, Inc.
40 Landsdowne Street
Cambridge
Massachusetts
USA

Date: 28-02-2005

Dear Sirs

We refer to the License, Development and Commercialisation Agreement between us dated 22 June, 2004 ("the Agreement") and in particular to Clause 8.1 (b) (i) of the Agreement. The capitalized terms used in this Letter, which are defined in the Agreement, will have the meanings given to them in the Agreement.

Notwithstanding the fact that the Transition Activities and Processes have not yet been completed by Millennium, the parties have agreed that GSK will pay to Millennium the milestone payment of nineteen million nine hundred thousand dollars (USD $19,900,000) referred to in Clause 8.1 (b