Biotech Stock Mailbag: Seattle Genetics

BOSTON (TheStreet) -- Clinical trial results and drug approval announcements move biotech stocks. With that reminder, Sandy L. kicks off this week's Biotech Stock Mailbag with a related question:

"I know you talk all the time about the importance of paying attention to FDA drug approvals and clinical trials. What are the biotech events on your radar screen right now?"

Seattle Genetics(SGEN) tops my list with two, potentially pivotal studies of two blood cancer drugs due to report results in the near future.

A phase II study of SGN-35 in Hodgkin's lymphoma is expected to read out in late September or October, said Seattle Genetics on a conference call Tuesday night. This phase II study is considered registration worthy because it's being conducted under a special protocol assessment (SPA) with the FDA. If the SGN-35 study is positive, Seattle Genetics intends to file for accelerated approval in the first half of 2011.

The phase II single-arm study enrolled about 100 patients with Hodgkin's lymphoma that continued to progress after two or three prior therapies. Look for a response rate from SGN-35 treatment in the range of 25-30% with durability of 4-6 months as an important demarcation of the drug's efficacy, although Seattle Genetics CEO Clay Siegall told me in an interview last week that FDA hasn't placed any specific response rate hurdle on the drug in the SPA.

A single-arm response rate study needs strong data to pass muster with FDA these days. A previous and smaller phase I study of SGN-35 in Hodgkin's patients showed a response rate of about 50%.

The second Seattle Genetics study that investors should be watching is a phase II study of SGN-33 in elderly patients with acute myeloid leukemia (AML). I'd consider this study the more risky of the two, given the need for SGN-33 plus chemotherapy to demonstrate a survival benefit over chemotherapy alone in a very sick patient population that has been difficult to treat effectively in studies of other drugs.

On Tuesday night's conference call, Seattle Genetics said to expect results from the SGN-33 study in late August through October. The data from this study were expected earlier so optimists will say the timeline slip could be due to the fact that SGN-33 treated patients are living longer. Or not. Be careful.