Updated from 2:22 p.m. Shares of Genta ( GNTA) were among the worst-performing health and pharmaceutical stocks Tuesday, falling 50% after the biopharmaceutical company said Sanofi-Aventis ( SNY) ended the companies' joint development agreement. The two companies will work together to develop Genasense, Genta's cancer drug, until May 8, 2005. After that, Genta will continue the development of the drug on its own. When the companies first entered the agreement in 2002, Aventis was seeking a late-stage development opportunity that could potentially be launched in the near term. Earlier this year, however, regulators rejected the drug with respect to melanoma. As a result, Aventis said that it could no longer support the development of Genasense. Shares of Genta traded down $1.30 to $1.30. Fonar ( FONR) rose 9.7% after the maker of MRI equipment swung to a first-quarter profit. The company posted a profit of 1 cent a share on sales of $25.1 million. A year ago the company posted a loss of 5 cents a share on sales of $13.3 million. Strong sales of the company's Upright MRI units led to the impressive first-quarter results. Shares traded up 11 cents to $1.25. Shares of BriteSmile ( BSML) fell 16.7% after the company posted weak third-quarter results and warned of a fourth-quarter shortfall as well. During the third quarter, the teeth-whitening technology company posted a loss of 24 cents a share on sales of $11.9 million. Analysts were expecting a loss of 9 cents a share on sales of $12.7 million. Looking ahead, BriteSmile forecast that fourth-quarter sales would decline both sequentially and on a year-over-year basis. Analysts had been expecting sales of $14.7 million. BriteSmile said the sales shortfall reflects soft demand experienced during the first part of the fourth quarter. Shares traded down $1.50 to $7.50.