The mistake all these conspiracy theorist make is that they say "BP will buy us and bury us" BP doesn't buy anything, individual pharma companies make acquisitions. And the individual pharma company that cures cancer will get an Amazon-like valuation.
The shares of other individual pharma companies may go down as they lose business to the cure, BP as a SECTOR may go down, but the Company with the cure will make hundreds of $billions and its stock will go to Jupiter.
And the CEO of that Company, who makes the decisions, will make $billions on his stock options. So don't worry, if this is the cure, someone will sell it to the public. That is the beauty of capitalism, folks!