(CNN)On bad days, Dewayne Johnson is too crippled to speak. Lesions often cover as much as 80% of his body.
Doctors have said they didn't expect him to live to see this day. But Monday marks a milestone: Johnson, 46, is the first of hundreds of cancer patients to see his case against agrochemical giant Monsanto go to trial.
CNN reported last year that more than 800 patients were suing Monsanto, claiming its popular weed killer, Roundup, gave them cancer.
Since then, hundreds more non-Hodgkin's lymphoma patients have made similar claims, Johnson's attorney, Timothy Litzenburg, said. He now represents "more than 2,000 non-Hodgkin's lymphoma sufferers who used Roundup extensively," he said.
Johnson, a father of two in California's Bay Area, applied Roundup weed killer 20 to 30 times per year while working as a pest manager for a county school system, his attorney said.
Johnson's case is the first to go to trial because, his doctors claim in court filings, he is nearing death. And in California, dying plaintiffs can be granted expedited trials.
And there's a lot riding on this case, which could set a legal precedent for thousands of cases to follow.
Report on Roundup ingredient in dispute
The big questions at stake are whether Roundup can cause cancer and, if so, whether Monsanto failed to warn consumers about the product's cancer risk.
In March 2015, the World Health Organization's International Agency for Research on Cancer (IARC) said the key ingredient in Roundup, glyphosate, is "probably carcinogenic to humans."
"For the herbicide glyphosate, there was limited evidence of carcinogenicity in humans for non-Hodgkin lymphoma," the report states.
"The evidence in humans is from studies of exposures, mostly agricultural, in the USA, Canada, and Sweden published since 2001. In addition, there is convincing evidence that glyphosate also can cause cancer in laboratory animals."
But Monsanto long has maintained that Roundup does not cause cancer, and that the IARC report is greatly outnumbered by studies saying glyphosate is safe.
"More than 800 scientific studies, the U.S. EPA (Environmental Protection Agency), the National Institutes of Health and regulators around the world have concluded that glyphosate is safe for use and does not cause cancer," Scott Partridge, Monsanto's vice president of strategy, said in a statement.
"We have empathy for anyone suffering from cancer, but the scientific evidence clearly shows that glyphosate was not the cause. We look forward to presenting this evidence to the court."
Monsanto spokeswoman Charla Lord said regulatory authorities help ensure Roundup is safe.
"The safety of each labeled use of a pesticide formulation must be evaluated and approved by regulatory authorities before it is authorized for sale," she has said.
The National Pesticide Information Center -- a cooperative between Oregon State University and the EPA -- said studies on cancer rates in humans "have provided conflicting results on whether the use of glyphosate containing products is associated with cancer."