http://www.fda.gov/cder/drug/cancer_endpoints/endpointsArtic...

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Note added at 16 mins (2005-09-25 03:06:01 GMT)
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Here is the explanation why it may be provisional - conditional

..Accelerated Approval or Subpart H Approval is a program described in the NDA regulations that is intended to make promising products for life threatening diseases available on the market on the basis of preliminary evidence prior to formal demonstration of patient benefit. The studies are designed to measure and the FDA evaluation is performed on the basis of a surrogate marker (a measurement intended to substitute for the clinical measurement of interest, usually prolongation of survival) that is considered likely to predict patient benefit. The approval that is granted may be considered a provisional approval with a written commitment to complete clinical studies that formally demonstrate patient benefit. The Federal Register published a discussion of Accelerated Approval with comments. Absent a formal demonstration of patient benefit, a risk benefit assessment cannot be made. Accelerated Approval designation does not necessarily lead to a Priority Review. Applications that were granted approval under the Accelerated Approval or Subpart H program in the Division of Oncology Drug Products are listed here.

http://www.accessdata.fda.gov/scripts/cder/onctools/Accel.cf...

http://www.fda.gov/cder/guidance/2197dft.pdf