CHICAGO (Reuters) - A jury in Chicago on Thursday rejected an Illinois woman's claim that the now discontinued heartburn drug Zantac caused her colon cancer, in the first trial out of thousands of lawsuits making similar allegations.

The jury in Cook County, Illinois circuit court agreed with arguments from drugmakers GSK and Boehringer Ingelheim that the plaintiff, 89-year-old Illinois resident Angela Valadez, had not proven her colon cancer was at least in part caused by her Zantac use.

Valadez had alleged that her cancer was a result of taking over-the-counter Zantac and generic versions of it from 1995 to 2014. The lawsuits over the drug say its active ingredient, ranitidine, under some conditions turns into a cancer-causing substance called NDMA.

Attorneys for Valadez had asked the jury to award $640 million for her suffering. The judge rejected Valadez's request to seek punitive damages during the trial, according to her attorneys.

(Reporting By Brendan Pierson in New York; Editing by Bill Berkrot)

By Diana Novak Jones