Projected 2018 sales:
$3.404 billion
2012 sales: $1.134 billion

Alexion Pharmaceuticals ($ALXN) may not have a huge market for Soliris, but it does have a recipe for success: an essential treatment for a frightening rare disease and a very, very hefty price tag.

Soliris was originally developed as a treatment for the life-threatening blood disorder paroxysmal nocturnal hemoglobinuria, a disease that only affects about 8,000 Americans. But at up to $400,000 per year, Soliris--recognized as the world's most expensive drug--doesn't have to reach many patients to hit the blockbuster threshold.

Soliris is Alexion's only source of revenue, so a March warning letter from the FDA detailing some problems at the Rhode Island plant where the drug is made was something to be taken very seriously. The company has hired some experts to help, and it has made sure the market knows that no finished product was contaminated and that there will be no resulting shortage of Soliris.

And Alexion has been branching out with the drug. It now has a designation as a treatment for atypical hemolytic uremic syndrome, a rare kidney disorder, and in June it won an orphan-drug designation for neuromyelitis optica, a serious neurological disorder that worsens with each attack. Between 2007, the year the drug launched, and 2012, its expanded market has broadened sales by 600%.

For more:
Booming Alexion looks to Ensemble platform for ultrarare disease programs
Rumors of big Roche bid for Alexion cool as analysts weigh in
Alexion brings in hired guns for troubled plant
Warning letter details contamination of Alexion's Soliris API
Alexion gets FDA warning but doesn't expect Soliris disruption