Genzyme Corp. announced Thursday that it has begun Phase IIIclinical trials of Thyrogen, its recombinant human thyroidstimulating hormone, in a multicenter trial of 100 to 150patients.

The hormone is given to thyroid cancer patients in conjunctionwith the synthetic thyroid hormones T3 and T4 while thepatients undergo tests.

Currently the diagnostic procedure involves whole-body scanswith radioiodine, said Genzyme spokeswoman Kathleen Riley.During that time the patients must discontinue their hormonesupplements in order for radioiodine uptake to occur. Duringthat seven- to 14-day period, the patients become hypothyroid,she said, and taking Thyrogen allows them to continue takingtheir hormone supplement while undergoing diagnostic testing.

Jim McCamant, editor of the Medical Technology StockNewsletter of Berkeley, Calif., said there is "not much of amarket" for Genzyme's recombinant hormone. New Yorkanalyst David Stone of Cowen & Co., however, is moreoptimistic. He estimated that the potential U.S. market forThyrogen is $25 million to $50 million.

"Thyrogen has a well-defined use, Genzyme has a strong patentposition, there aren't any competitors, and the initial data lookencouraging," he said. The Cambridge, Mass., company's stock(NASDAQ:GENZ) is currently Stone's No. 1 pick. The company'sshares were up $1 to $42.50 a share on Thursday. -- JenniferVan Brunt

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