The company that showed biotech investors how a single drug can produce gaudy returns is out to justify how four drugs can warrant an $80 billion market cap.

In the third quarter, Amgen (NASDAQ:AMGN) earned $612 million, or $0.46 per share. The world's largest biotech company also reported product sales growth of 54% to $2.1 billion, driven by growth across all three drug franchises.

One of the primary drivers for growth was Aranesp, an anemia drug that saw sales jump 284% from last year's quarter to $324 million. Its predecessor, Epogen, gained 12% to $626 million in the quarter.

Combined sales of Neulasta and its predecessor Neupogen, which help prevent chemotherapy-related infections, grew 39% to $657 million. Sales of Enbrel, the rheumatoid arthritis drug Amgen gained in its acquisition of Immunex, more than doubled to $342 million.

At a little over 30x this year's earnings, Amgen now looks reasonably priced, if it didn't just a few years ago. The gaudy sales growth has generated in excess of $2 billion in annual free cash flow, which the company has used to repurchase shares. Through the first three quarters this year, the company has repurchased 20 million shares for $1.2 billion, or about $60 a share.

So it would appear that Amgen's production might actually justify the promise priced into the shares of younger biotechs we've covered in the past, such as Millennium Pharmaceuticals (NASDAQ:MLNM), Human Genome Sciences (NASDAQ:HGSI), Vertex Pharmaceuticals (NASDAQ:VRTX), and Medarex (NASDAQ:MEDX). Even Genentech (NYSE:DNA) seems to have promise priced into it.

Going forward, Amgen raised full-year, combined Epogen/Aranesp sales guidance from between $3.7 and $3.9 billion to between $3.8 and $4.0 billion. In addition, it narrowed total product sales guidance to between $7.6 and $7.9 billion from a wider range of $7.5 to $8.0 billion.

Following yesterday's announcement, shares of Amgen are down 5% to $60.41 in early afternoon trading.

Jeff Hwang can be reached at JHwang@fool.com.