“There’s just no possibility, no rational way this could happen,” he said.

Elisabeth Bik, a leading expert in image manipulation, became aware of the company last summer after short sellers filed the F.D.A. petition. In a series of twitter posts, posts on her blog and on the website PubPeer, Dr. Bik has pointed to signs that she said show some results had been copied and pasted from other experiments.

“Those were of severe concern,” she said in an interview. Based on the pattern of irregularities in images in multiple papers, she believes “it is highly likely that there was some manipulation going on.”

Charles Spruck, a cancer researcher at the Sanford Burnham Prebys Medical Discovery Institute in San Diego, who has more than 25 years of experience with the Western blot method, said he believed the anomalies in those images could be the result of simple mistakes or vagaries of the technique.

Irregularities or errors in one or two images could be due to chance, but “when you see it again and again, it makes it unlikely that you could do it accidentally,” said Dr. David Vaux, deputy director of scientific integrity and ethics at the Walter and Eliza Hall Institute of Medical Research in Australia.

Mr. Barbier dismissed the criticisms, saying that the irregularities did not impact the company’s research findings. “These background pixels have no impact on the data or its interpretation,” he said, adding “We stand by Professor Wang 100 percent.”

Dr. Vaux and others bemoaned the limitations of peer review in identifying mistakes or manipulation, and said many scientific journals are reluctant to retract papers because of their fear of being sued, or damage to their own reputations.

“It’s time for regulatory bodies to step in, as it seems that the peer review process has taken it as far as it can,” Dr. Hu said. “If the tide has shifted such that the science seems to not be there, I just don’t see how the clinical trials can proceed.”