July has been a good month for biotech investors. Share prices in the biotech sector as measured by the NYSE Biotechnology Index are up 24% compared to the 6.6% gain for the S&P 500. Earlier in the month, Amgen( ) reported better-than-expected results from a trial of its experimental bone-protecting drug denosumab in patients with advanced breast cancer. Amgen's shares vaulted 16% on the news.

In the week just ended, the momentum in biotech shares has continued further. While a host of favorable clinical trial results was the bigger driver, a large buyout announcement added the icing to the cake.

Clinical Trial Results

Bringing back memories of the dotcom era, shares of Human Genome Sciences ( ) rose nearly 300% to $12.50 a share after the company reported favorable results for its experimental lupus drug Benlysta. Targacept (TRGT) shares more than doubled to $7.25 a share after its depression drug candidate met its goals in a mid-stage trial. Onyx Pharmaceutical ( ) reported encouraging results for its breast cancer treatment Nexavar to push its shares higher by 21%. Shares of Celgene ( ) jumped nearly 16% after the company announced significant improvement in progression-free survival of patients taking Revlimid as a first-line treatment for multiple myeloma.