AFFX Affymetrix, Inc.

Affymetrix Inc., (Nasdaq:AFFX) announced today that scientists at Cancer Research UK have used Affymetrix technology to discover the molecular basis for tamoxifen response in breast cancer cells - and the reason why some women can develop resistance to the treatment. Their findings are published in Nature1. Tamoxifen is given to most women for five years after they are first diagnosed with breast cancer to help prevent the disease from coming back. Some women develop resistance to the treatment after time, meaning their cancer is more likely to return. Researchers at the Cancer Research UK Cambridge Research Institute have discovered for the first time the mechanism by which the breast cancer therapy tamoxifen operates. It switches off a breast cancer gene ErbB2 via a protein called Pax2. Pax2 acts as a 'switch' to keep ErbB2 switched off. Tamoxifen resistance occurs when ErbB2 remains switched on. Previously it was known that tamoxifen worked by blocking estrogen from causing unchecked cell growth in breast cancer by switching certain genes on, but the mechanism by which this occurred was unknown. "We knew that women developed resistance to tamoxifen but previously our understanding of why this occurred could be compared with trying to fix a broken car without knowing how the engine worked,� said Dr Jason Carroll, lead author on the study. �Now we understand how all the engine parts operate and we can start to think about ways to make repairs.� "Using the GeneChip� Human Tiling 2.0R Array Set, we have discovered that for tamoxifen to work it has to block the gene ErbB2. It does this by using a control switch that is hidden in the background of the genome, within the ErbB2 gene itself. In order for tamoxifen to be effective, this switch must be held in the off position by Pax2. Now we understand how women can develop tamoxifen resistance." The production of estrogen can cause breast cancer cells to grow and divide and tamoxifen prevents estrogen from causing breast cancer cells to grow, helping to lower the risk of the disease returning. Most women have breast cancers that are stimulated to grow by estrogen, but not all. Breast cancer is the most common cancer among American women. More than 250,000 new cases will be diagnosed this year, and more than 40,000 women will die from the disease in 2008, according to the American Cancer Society. There are currently about 2.5 million survivors in the country2. "Cancer Research UK's early clinical trials of tamoxifen helped transform the way that women were treated for early breast cancer, saving tens of thousands of lives, and this work is yet another step forward,� said professor Sir David Lane, Cancer Research UK's chief scientist. "More women are surviving breast cancer than ever before thanks to improvements in diagnosis and treatment as well as fundamental science discoveries like this." "Tamoxifen has been a huge success story helping to prevent breast cancer recurring for many women,� added Lane. �Understanding why it occasionally stops working is really important because it allows us to identify new targets for drug development and who will need such treatments." �GeneChip� Tiling Arrays have enabled high-resolution, genome-wide mapping of estrogen receptor (ER) binding sites,� said Kevin King, president of Affymetrix. �This study demonstrates the power of using this approach to resolve a single important ER binding site that plays a key role in determining the mechanisms underlying tamoxifen resistance in breast cancer. It has the potential to significantly improve prescription decisions related to this leading drug treatment.� 1Hurtado A., et al. ERBB2 regulation by Estrogen Receptor-Pax2 determines tamoxifen response, Nature. November 12 2008. 2From the American Cancer Society webpage: What Are the Key Statistics for Breast Cancer? http://www.cancer.org/docroot/CRI/content/CRI_2_4_1X_What_are_the_key_statistics_for_breast_cancer_5.asp?sitearea= About Affymetrix Affymetrix GeneChip� microarray technology is the industry-standard tool for analyzing complex genetic information. After inventing microarray technology in the late 1980s, Affymetrix scientists have been dedicated to developing innovative products that provide researchers with a more complete view of the genome. These products continue to accelerate genetic research and enable scientists to develop diagnostics and tailor treatments for individual patients by identifying and measuring the genetic information associated with complex diseases. Today, Affymetrix technology is used by the world�s top pharmaceutical, diagnostic and biotechnology companies, as well as leading academic, government and not-for-profit research institutes. More than 1,800 systems have been shipped around the world and more than 14,000 peer-reviewed papers have been published using the technology. Affymetrix is headquartered in Santa Clara, Calif., and has manufacturing facilities in Sacramento, Calif., Cleveland, Ohio, and Singapore. The company has about 1,100 employees worldwide and maintains sales and distribution operations across Europe and Asia. For more information about Affymetrix, please visit the company�s website at www.affymetrix.com. About Cancer Research UK Together with its partners and supporters, Cancer Research UK's vision is to beat cancer. Cancer Research UK carries out world-class research to improve understanding of the disease and find out how to prevent, diagnose and treat different kinds of cancer. Cancer Research UK ensures that its findings are used to improve the lives of all cancer patients. Cancer Research UK helps people to understand cancer, the progress that is being made and the choices each person can make. Cancer Research UK works in partnership with others to achieve the greatest impact in the global fight against cancer. For further information about Cancer Research UK's work or to find out how to support the charity, please call 011 44 20 7009 8820 or visit www.cancerresearchuk.org. Forward-looking Statements All statements in this press release that are not historical are �forward-looking statements� within the meaning of Section 21E of the Securities Exchange Act as amended, including statements regarding Affymetrix� �expectations,� �beliefs,� �hopes,� �intentions,� �strategies� or the like. Such statements are subject to risks and uncertainties that could cause actual results to differ materially for Affymetrix from those projected, including, but not limited to: risks and uncertainties relating to commercial success of the agreement with Cancer Research UK discussed in this press release; risks of the company�s ability to achieve and sustain higher levels of revenue, higher gross margins and reduced operating expenses; uncertainties related to technological approaches, manufacturing and product development; personnel retention; uncertainties related to cost and pricing of Affymetrix products; dependence on collaborative partners; uncertainties related to sole-source suppliers; risks associated with past and future acquisitions; uncertainties relating to FDA and other regulatory approvals; competition; risks relating to intellectual property of others and the uncertainties of patent protection and litigation. These and other risk factors are discussed in Affymetrix� Form 10-K for the year ended December 31, 2007, and other SEC reports, including its Quarterly Reports on Form 10-Q for subsequent quarterly periods. Affymetrix expressly disclaims any obligation or undertaking to release publicly any updates or revisions to any forward-looking statements contained herein to reflect any change in Affymetrix� expectations with regard thereto or any change in events, conditions or circumstances on which any such statements are based. NOTE: Affymetrix, the Affymetrix logo and GeneChip� are registered trademarks owned or used by Affymetrix Inc.