This week, Wood Mackenzie, an Edinburgh-based research and consulting firm, reviews recent trends in biotechnology stocks.

The Nasdaq Biotechnology Index made no progress during July and August, and stands only marginally higher than it did at the start of the year. Broader market indices lost value during the period.

Bad news continued for California-based Amgen over this period. On 30 July, US reimbursement authorities issued a ruling that will reduce the use of erythropoietin for treating anaemia in patients with cancer in the Medicare and Medicaid programmes. That adds to the pressures building up on Amgen's flagship erythropoietin drug, Aranesp, which is embroiled in safety concerns and losing sales (see Nature 448, 121; doi:10.1038/448121b 2007).

Then on 15 August, Amgen announced a 14% reduction in its workforce — much of which is likely to be in its research-and-development staff. The company's share price has continued to fall. Over the past two months it has dropped nearly 10%; its value is now at its lowest point for more than four years.

Amgen's misfortunes were offset by strong performances by other companies in the index. At the end of July, when reporting its second quarter results, Vertex of Cambridge, Massachusetts, announced good results from clinical trials of its experimental hepatitis C drug, telaprevir — widely viewed as a potential blockbuster. The company's share value climbed by around 35% over the period.

The stock of Onyx Pharmaceuticals in Emeryville, California, has also climbed steadily. In August, its marketing partner Bayer reported stronger-than-expected sales of its newly approved kidney-cancer drug Nexavar (sorafenib). The drug also achieved impressive clinical results for the treatment of liver cancer, potentially broadening its market.