SAN FRANCISCO — Monsanto Co. has lost out on an early bid to knock out more than 400 federal cases claiming that the active ingredient in its Roundup herbicide causes a type of cancer.

In what he called “a very close question,” U.S. District Judge Vince Chhabria of the Northern District of California, who is overseeing the cases, declined to grant Monsanto’s motion for summary judgment that plaintiffs couldn’t prove that the glyphosate in Roundup causes non-Hodgkin lymphoma (NHL), a type of cancer affecting white blood cells. Although Chhabria wrote that evidence plaintiffs put forward “seems too equivocal to support any firm conclusion that glyphosate causes NHL,” he found that they could put on admissible evidence that could convince a reasonable jury to conclude otherwise.