USPS issued the following press release: 

A four-year extension of the Breast Cancer Research (BCRS) semipostal stamp has been approved beyond Dec. 31, 2007.

Legislation passed recently by Congress and signed by President George W. Bush granted the extension.

Since the stamp first went on sale in 1998, the Postal Service has sold more than 802 million stamps, raising $59.5 million for breast cancer research.

Semipostal stamps are First-Class Mail postage stamps that are issued and sold by the Postal Service at a price above the First-Class Mail single-piece first-ounce rate to raise funds for designated causes.