Evidence that Roundup weed killer can cause cancer seems weak," but experts can still make that claim at trial, a U.S. judge ruled Tuesday. The decision by U.S. District Judge Vince Chhabria in San Francisco allows hundreds of lawsuits against Roundup's manufacturer, Monsanto, to move forward. The lawsuits by cancer victims and their families say the agrochemical giant long knew about Roundup's cancer risk but failed to warn them. The judge wanted to determine whether the science behind the claim that Roundup can cause non-Hodgkin's lymphoma had been properly tested and met other requirements to be considered valid. Before issuing his ruling, Chhabria spent a week in March hearing dueling testimony from epidemiologists. He peppered them with questions about potential strengths and weaknesses of research on the cancer risk of glyphosate. Beate Ritz, an epidemiologist at the University of California, Los Angeles, testified for the plaintiffs that her review of scientific literature led her to conclude that glyphosate and glyphosate-based compounds such as Roundup can cause non-Hodgkin's lymphoma. Ritz said a 2017 National Institute of Health study that found no association between glyphosate and non-Hodgkin's lymphoma had major flaws. A federal judge in Sacramento in February blocked California from requiring that Roundup carry a label stating that it is known to cause cancer.