The drug is just barely off and running and the treatment is not inexpensive by any means and according to this notice put out by the FDA, they want additional 
information at CMS on how stroke victims are affected that have received the drug so this appears to be further exploration into the world of immunotherapy treatment to determine what effects and benefits are potentially available with strokes being on the list.
Dendreon Announces CMS Evaluation of Provenge for Late Stage Prostate Cancer Patients
As I wrote back in March before the approval process took place, part of the evaluation from the FDA included looking at their sophisticated tracking system called “Intellivenge”. 
Dendreon “Intellivenge” Algorithmic Software Supporting Administration of Provenge – Seeking FDA Approval by May 1st
Dendreon uses a sophisticated tracking system with bar coding to ensure the correct blood is returned to the right patient after the incubation process. This is important as someone would not want the blood from another patient, although I read it would not be fatal, but rather not as effective but still no room for error here.
This is a brand new class of drugs and It appears to be a good question to find out what other uses and benefits may be derived with measuring additional potential benefits. BD
The Centers for Medicare and Medicaid Services (CMS) has called this meeting to consider the currently available evidence regarding the impact of labeled and unlabeled use of autologous cellular immunotherapy treatment on health outcomes of patients with metastatic prostate cancer.
As described on the FDA website at http://www.fda.gov/BiologicsBloodVaccines/CellularGeneTherapyProducts/ApprovedProducts/ucm213559.htm, “PROVENGE® (Sipuleucel T, APC8015) is an autologous cellular immunotherapy product consisting of peripheral blood mononuclear cells (PBMCs) obtained from patients by leukapheresis and activated in vitro with a recombinant fusion protein (prostatic acid phosphatase fused with GM-CSF). FDA will require the sponsor to complete a post marketing study to evaluate the risk of stroke in patients who receive sipuleucel-T.”
Provenge® has FDA approved labeling for the treatment of asymptomatic or minimally symptomatic metastatic castrate resistant (hormone refractory) prostate cancer.
Centers for Medicare & Medicaid Services