A February 17, 2006 article by Karen Matthews in The Repository quotes ACSH's Dr. Ruth Kava:
Artificial sweeteners have had a controversial history. Cyclamates were banned in 1970 after they were linked with cancer in rats, and one 1970s study found that rats given the equivalent of the saccharin contained in 800 to 1,000 cans of soda per day had an increased risk of bladder cancer.
Ruth Kava, director of nutrition for the American Council on Science and Health, says that after later research on saccharin found that the cancer link "was only in rats and only in male rats" the warning label was taken off.
As for Splenda, Kava says it appears to be safe. "The FDA really does require these things to be tested before they re on the market," she says.