Herceptin - $1.66 billion

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Herceptin

Company: Genentech
2011 sales: $1.66 billion
Developer: Genentech
FDA approvals: Metastatic HER2-positive breast cancer, 1998; adjuvant in early-stage HER2-positive breast cancer, 2006; additional adjuvant approvals, 2008; HER2-positive gastric or gastroesophageal junction cancer

Herceptin is only 14 years old, and it already has a legacy. It was the first targeted cancer drug, aimed at patients whose tumors have specific genetic characteristics. In this case, the appropriate patients have tumors that over-express the HER2 gene. When Herceptin launched, personalized medicine was officially under way.

Since then, other targeted drugs have hit the market, including epidermal growth factor receptor inhibitors such as AstraZeneca's ($AZN) Iressa, Amgen's ($AMGN) Vectibix, and Bristol-Myers Squibb's ($BMY) Erbitux (No. 7 on our list). So far, none has surpassed Herceptin, sales-wise. As of 2008, more than 420,000 women had been treated with Herceptin worldwide. And with the discovery that HER2 is key in other cancers, Herceptin's use may only grow; in late 2010, it won FDA approval for gastric cancers over-expressing HER2.