Updated from 2:37 p.m. EDT

Shares of Isolagen ( ILE) were among the worst-performing health-related stocks Monday, falling 25% after the company announced the resignation of its chief executive.

Robert Bitterman, who joined the company in September 2004, served as CEO for less than eight months. The company did not offer an explanation for Bitterman's departure. The news comes just a week after the company appointed a new chief financial officer. Isolagen has retained recruiting firm Borman, Golding to assist the company in finding and hiring a new chief executive to succeed Bitterman. Shares traded down $1.47 to $4.41.

Adventrx Pharmaceuticals ( ANX) traded actively after the company received Food and Drug Administration clearance to begin a phase III clinical trial of its CoFactor treatment for metastatic colorectal cancer. CoFactor is designed to enhance the activity of the widely used cancer drug 5-fluorouracil. The study is expected to include about 600 patients, half of whom will receive a CoFactor combination therapy. The primary endpoint for the study is progression free survival, which is defined as the time from start of treatment to time of disease progression or death. Shares traded down 7 cents to $2.78 on volume of 2.1 million shares.

Shares of Sepracor ( SEPR) rose 1.6% after the company posted a first-quarter loss that was smaller than expected. The pharmaceutical company posted a loss of $22.6 million, or 22 cents a share, on sales of $119 million. Analysts polled by Thomson First Call were expecting a loss of 60 cents a share on sales of $111 million. A year ago, the company posted a loss of $50.4 million, or 59 cents a share, on sales of $99.5 million. Last year's results included a charge of $30.7 million, or 36 cents a share. Shares traded up 97 cents to $61.25.

Endologix ( ELGX) fell 4.4% after the medical device maker posted a wider first-quarter loss. The company reported a loss of $3.3 million, or 10 cents a share, on sales of $1.4 million. Analysts were expecting a smaller loss of 8 cents a share on sales of $1.7 million. A year ago, the company posted a loss of $2 million, or 7 cents a share, on sales of $820,000. Endologix said the wider year-over-year loss was caused by costs associated with the build out and training of its domestic sales force and by expenses related to Sarbanes-Oxley compliance. Shares traded down 22 cents to $4.83.

Other health-care volume movers included Pfizer ( PFE), down 19 cents to $27.03; Elan ( ELN), up 20 cents to $4.06; Amgen ( AMGN), down 86 cents to $58.03; Merck ( MRK), down 28 cents to $33.92; Johnson & Johnson ( JNJ), up 5 cents to $68.54; Schering-Plough ( SGP), down 5 cents to $20.70; Intuitive Surgical ( ISRG), down $2.28 to $43.50; and Genentech ( DNA), down 41 cents to $69.43.

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