Which Big Biotechs join Gilead in Fortune's fastest-growing pharma ranks?

The company at the top of Fortune's fastest-growing-in-pharma list is just the one you'd expect: Gilead Sciences ($GILD), with its hep C-fueled leap into the industry's top 10 by revenue. And it's no surprise that the next two are Big Biotech companies, given the ascendance of biologic meds. But one Big Pharma--and only one--managed to crack the top 5.

How? By snapping up a rival in one of 2009's megadeals. Its big-time acquisition helped push sales up by more than 75% between 2009 and 2011--and countered recent slippage to generate a 5-year annual growth rate of 9%.

No, it's not Pfizer ($PFE), with its Wyeth buyout, or Roche ($RHHBY) and its Genentech purchase. It's Merck & Co. ($MRK), whose Schering-Plough buyout quickly boosted sales (and touched off a series of cost-cutting drives, of course). The company has since suffered on generic competition for its allergy-and-asthma med Singulair, but it's engineering a comeback on cancer immuno-therapy Keytruda and a forthcoming hepatitis C cocktail.

Allergan ($AGN) came by its fourth-place slot with a 5-year annual growth rate of 10%, thanks to its pipeline-in-a-drug Botox--which now boasts a slate of medical indications in addition to its best-known approvals as a cosmetic injection--and other top-selling drugs. That growth is, of course, the reason Actavis was so eager to snatch up the company in a $66 billion deal that closed in March--and its brand will live on, now that Actavis shareholders adopted the name as its own.

That brings us to the top three fastest-growing pharmas in the Fortune 500. And they're all biotech. Biogen $BIIB) is in third place with a 5-year growth rate of 17.3% and 2014 revenue of $9.7 billion. Its new multiple sclerosis pill Tecfidera played a big role in that growth, and the drug is expected to keep on giving in that department, with $4.1 billion in forecasted 2015 sales.

In second place, Celgene ($CELG), whose blood cancer treatment Revlimid just can't be stopped (at least not till biosimilars appear on the scene in the coming years). With a 5-year annual growth rate of 23.3% and $7.7 billion in 2014 revenue, the company is on its way to CEO Bob Hugin's ambitious goal of $12 billion in sales by 2017. Revlimid accounted for almost $5 billion of that 2014 revenue, and it has since won a new indication in newly diagnosed multiple myeloma patients. EvaluatePharma predicts $8 billion-plus in Revlimid sales by 2020.

And of course we have Gilead at the top of the heap. Already a formidable antiviral company before its hep C treatments came along, Gilead has made big headlines with its lickety-split launches of Sovaldi and Harvoni, which pushed 2014 revenue to $24.9 billion. With a 5-year growth rate of 28.8%, Gilead is expecting a bit of a slowdown in growth this year compared with last--with rival AbbVie ($ABBV) now on the hep C scene, discounting is taking a toll on sales--but still expects up to $29 billion in 2015 sales.

- see the Fortune ranking

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