(Bloomberg) -- Nektar Therapeutics had the worst day in over five years for an S&P 500 Index member.
The biopharmaceutical firm lost 41.8 percent of its value on Monday after response rates in melanoma and kidney cancer patients decreased in a mid-stage trial of the company's cancer drug in combination with Bristol-Myers Squibb Co.'s Opdivo. That's the biggest one-day loss by an S&P 500 Index constituent in more than five years, according to data compiled by Bloomberg.
San Francisco-based Nektar's plunge shattered the previous record for the period. Williams Cos., an energy infrastructure company, fell by 34.8 percent in a single day in 2016.
--With assistance from Yu Lung Law and Tatiana Darie.
To contact the reporter on this story: Brandon Kochkodin in New York at bkochkodin@bloomberg.net
To contact the editor responsible for this story: Joe Weisenthal at jweisenthal@bloomberg.net
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