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      &lt;font style="FONT-FAMILY: Times New Roman, Times, serif; FONT-SIZE: 10pt"&gt;Because

      of our historically significant net operating losses, we have

      not paid income taxes since inception. We maintain deferred

      tax assets that reflect the net tax effects of temporary

      differences between the carrying amounts of assets and

      liabilities for financial reporting purposes and the amounts

      used for income tax purposes. These deferred tax assets are

      comprised primarily of net operating loss carryforwards and

      also include amounts relating to nonqualified stock options

      and research and development credits. The net deferred tax

      asset has been fully offset by a valuation allowance because

      of the uncertainty of our future profitability and our

      ability to utilize the deferred tax assets. Utilization of

      operating losses and credits may be subject to substantial

      annual limitations due to ownership change provisions of

      Section 382 of the Internal Revenue Code. The annual

      limitation may result in the expiration of net operating

      losses and credits before utilization.&lt;/font&gt;

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