SAN FRANCISCO (CN) – Concluding a second round of expert testimony on the alleged link between non-Hodgkin lymphoma and Monsanto’s popular weed killer Roundup, a scientist said Friday that a new study finding no link between the two is flawed.
Cancer expert Christopher Portier testified that the 2018 study published in the Journal of the National Cancer Institute suffered from measurement errors, leading its authors to conclude that there is no association between cancer in humans and glyphosate, the active ingredient in Roundup.
“From the faulty analysis they conducted they saw nothing,” Portier said. “You see what you would expect to see because of the exposure misclassification.”
Portier’s testimony could advance more than 300 lawsuits filed against Monsanto and consolidated in a multidistrict case in San Francisco. The suits were filed by farmers and landscapers who say exposure to glyphosate caused them to develop non-Hodgkin lymphoma, or cancer of the lymph nodes.
U.S. District Judge Vince Chhabria will decide what expert testimony a jury should hear based on whether the experts’ claims meet rigorous scientific standards.
In 2015, the World Health Organization’s International Agency for Research on Cancer concluded that glyphosate is “probably carcinogenic to humans.”
Last month, Monsanto presented its expert Christopher Corcoran, a biostatistician who poked holes in the IARC study on which Portier was an adviser. Corcoran objected to Portier’s use of meta-analysis, a statistical technique that combines results from different studies and clinical trials to get a clear answer. He called it a “seriously flawed” approach that can lead to “spurious associations.”
Portier addressed the meta-analysis on Friday, confirming that his view of the link between glyphosate and non-Hodgkin lymphoma is “mostly driven” by its results, and that it did not include the 2018 study.
The 2018 study is commonly referred to as the Andreotti study, after its principal author, Gabriella Andreotti, an epidemiologist at the National Cancer Institute in Washington.
Portier said he would not include the Andreotti study in a meta-analysis both due to its “failures” and because its approach is so different from those of other epidemiological studies on the subject.
“After looking at the Andreotti study…I believe the strength of the observed association [between glyphosate and non-Hodgkin lymphoma] is high enough to warrant a strong opinion there,” Portier said. “We have epidemiological studies – or evidence in the real world – in real people at current exposures.”
Chhabria asked Portier to discuss latency, the time between initial carcinogen exposure and when cancer is diagnosed.
The concern is that case-control studies looking at possible connections between glyphosate and non-Hodgkin lymphoma looked at patients with latency periods of as little as seven years.
Chhabria pointed out that some patients who participated in the studies had been diagnosed with non-Hodgkin lymphoma in the early 1980s, and Roundup came on the market in 1974.
“With these studies we tend to prefer longer periods between exposure and diagnosis, and if we don’t have long periods between exposure and diagnosis, we are concerned that perhaps the disease was caused by something else,” Chhabria said. “And so the first question you might ask is, well maybe the pesticide that people were using before they started using glyphosate was the pesticide that caused NHL.”
Portier replied that some of the patient cohorts had latency periods of 10 to 12 years. He said the studies represent up to 4 million people, “and from such a large draw you can get the people who have really sharp latencies and you can really see the effects.”
He added that one study finding a link between glyphosate and non-Hodgkin lymphoma had adjusted for 48 pesticides, rendering latency less important.
“Unless there’s a phantom pesticide out there causing the NHL, then seeing the NHL [in the study] should worry you,” Portier said. “If you hadn’t seen it, you might say it wasn’t long enough. But having adjusted for everything, I would have to conclude that is a real NHL pesticide.”
Glyphosate is the most widely used agrichemical in history. Monsanto introduced it in 1974, and its use exploded in 1996 after Monsanto introduced “Roundup-ready” seeds engineered to resist glyphosate. More than 2.6 billion pounds of glyphosate were spread on U.S. farmlands and yards between 1992 and 2012, according to the U.S. Geological Survey.
The alleged connection between glyphosate and non-Hodgkin lymphoma, along with the science behind it, has been heavily disputed.
Although the International Agency for Research on Cancer concluded that glyphosate is likely carcinogenic, the U.S. Environmental Protection Agency reached the opposite conclusion last year.