With the general markets sliding last week over concerns about an uncertain economy, biotech companies followed suit and by close of market Thursday, the BioWorld Blue Chip Biotech Index had dropped almost 1 percent since the start of the month. This was, however, slightly better than the 1.5 percent decline in the Nasdaq Composite Index over the same period, while the Dow Jones Industrial average has so far held its own and remained unchanged.

Leading the decliners so far in May has been Seattle Genetics Inc., whose shares have fallen 8.7 percent despite reporting solid revenue growth in its first quarter results with net product sales of its Adcetris (brentuximab vedotin) antibody-drug conjugate for treating Hodgkin's lymphoma and anaplastic large-cell lymphoma coming in at $38.7 million compared to $33.9 million for the same period in 2013. Despite the fact that most analysts believe the company's prospects are very good going forward investors are still looking for more. It is a story that has been reflected across the whole spectrum of the sector – despite a generally positive first quarter for public biotech companies, the reports have failed to bring investors back to the fold. (See BioWorld Blue Chip Index, below.)

The BioWorld Growth Index, which includes companies with market caps in the range of $1 billion to $3 billion and a résumé that typically includes a strong drug pipeline and partnered products in late-stage clinical trials, has seen its value drop almost 8 percent since the end of the first quarter, but similar to the Blue Chip Index has only fallen a little over 0.5 percent in May. However, companies in the group have seen their share values go on a wild ride during this period of uncertainty for the sector.

Leading RNAi therapeutics company Alnylam Pharmaceuticals Inc., for example, saw its share value drop 15 percent in April only to regain most of it back so far this month on the strength of reporting positive top-line results from its ongoing phase I trial of ALN-AT3, a subcutaneously administered RNAi therapeutic targeting antithrombin in development for the treatment of hemophilia and rare bleeding disorders.

Among the leading decliners in the group was Aegerion Pharmaceuticals Inc., of Cambridge, Mass., whose shares have tumbled 25 percent after posting a wider loss than analysts were expecting in its first quarter financials. The company did post $27 million in net product sales for its Juxtapid (lomitapide) capsules, approved to treat patients with homozygous familial hypercholesterolemia (HoFH), a genetic disorder that causes extremely high cholesterol levels. The amount represented a growth of 24 percent over net product sales from the U.S. business in the prior quarter.

News of Acorda Therapeutics Inc.'s complete response letter for the new drug application (NDA) related to Plumiaz (diazepam) for epileptic cluster seizures was enough to send its shares down about 14 percent so far this month. The company also said the nasal spray version of the benzodiazepine therapy is unlikely to win approval this year. (See BioWorld Today, May 5, 2014.)

The dive in share prices permeated across the board for all biotech companies. The BioWorld Emerging Biotech Index, which tracks selected small-cap companies that have market caps averaging about $500 million, has seen its value drop about 1 percent in May.

Despite a rocky start to the month, the overall declines for biotech companies have not been as dramatic as predicted. There will still be some turbulence going forward but with investors squarely focused on the upcoming 50th meeting of the American Society of Clinical Oncology later this month this could be enough to smooth the ride for biotech stocks given the number of promising results from important cancer therapies that drug developers are scheduled to report.