June 1 (Reuters) - A Delaware judge has allowed more

than 70,000 lawsuits over discontinued heartburn drug Zantac to

go forward, ruling that expert witnesses can testify in court

that the drug may cause cancer.

The ruling on Friday by Judge Vivian Medinilla of the

Delaware Superior Court in Wilmington is a setback for former

Zantac makers GSK, Pfizer ( PFE ), Sanofi and

Boehringer Ingelheim, which had argued that the expert

witnesses' opinions lacked scientific support.

Medinilla wrote that the strength of each sides' scientific

arguments should be decided by juries.

"Delaware courts are loath to step into the heart of

technical debate between opposing scientists," she said.

"This moves us one step closer to justice for our clients,"

Brent Wisner, one of the plaintiffs' lead lawyers, said in a

statement on Saturday.

GSK, Pfizer ( PFE ) and Sanofi said in separate statements that they

disagreed with the decision and would appeal. They said there

was no reliable evidence showing Zantac caused cancer. A

spokesperson for Boehringer Ingelheim did not immediately

respond to a request for comment.

In 2019, some manufacturers and pharmacies halted Zantac

sales after a chemical called NDMA, which is known to cause

cancer, was detected in some pills. Some tests showed that

Zantac's active ingredient, ranitidine, could degrade into NDMA

over time or when exposed to heat.

Lawsuits began piling up from people who said they developed

cancer after taking Zantac. Plaintiffs said the companies knew,

or should have known, that ranitidine posed a cancer risk and

that they failed to warn consumers.

The U.S. Food and Drug Administration asked manufacturers to

pull the drug off the market in 2020. The drugmakers have

maintained that there is no evidence Zantac exposed users to

harmful levels of NDMA.

Medinilla is presiding over the majority of nearly 80,000

cases still pending in the United States over Zantac, which was

once the world's top-selling drug.

In addition to the cases in Delaware, the drugmakers are

facing about 4,000 claims in California state court and about

2,000 in various other state courts around the country.

Last month a jury in Chicago rejected an Illinois woman's

claim that Zantac caused her colon cancer, handing GSK and

Boehringer Ingelheim a victory in the first case to go to trial.

The drugmakers notched a significant win in 2022, when

another judge dismissed about 50,000 lawsuits making similar

claims that had been consolidated in federal court in Florida.

That judge concluded that the opinions of the plaintiffs'

expert witnesses that Zantac can cause cancer were not supported

by sound science. Plaintiffs are appealing that ruling, which

concerns different experts from those in the Delaware case.

1988 and one of the first-ever drugs to top $1 billion

in annual sales. Originally marketed by a forerunner of GSK, it

was later sold successively to Pfizer ( PFE ), Boehringer and finally

to Sanofi.