Wrong, Dendreon went way up once it gained approval. Just look at a historical chart for the stock. In the end the company failed despite approval because of the high cost of treatment, but not because of manipulation. Once it seems clear to the market that money is going to start flowing in, as it did once Dendreon gained FDA approval, manipulation is no longer viable due to greatly increased trading volume.
Correction: Dendreon went way up (from sub $5 to $30pps range) after Phase III results were reported in April 2009. Once final approval came through a year later it bumped up into the $40pps range. It then crashed a little over a year after approval once it became clear that the company wasn't going to be able to execute its business plan for the drug due to high costs.