But yesterday, scientists cited "major flaws" in the study, criticising the size of the test groups and questioning the link between treatment and effect.
Mark Vickers, a senior research fellow at the University of Auckland, said he was surprised the paper was published without key data gauging fluid intakes and body growth.
Dr Vickers said the strain of rat used in the trials was prone to developing tumours with advancing age anyway.
University of Auckland professor of biostatistics Dr Thomas Lumley believed the strongest conclusion that could be drawn from the study was that it would be worth studying a larger group of controls, and just a single low dose of Roundup or GM corn.
But Organic New Zealand spokeswoman Debbie Stanwick said she would not be surprised if the claims were genuine.
"You can't keep putting something which isn't natural and has been doused in herbicide into your body - it's not rocket science."
The report
* Rats in groups of 10 were tested over two years with maize genetically modified to be tolerant to the herbicide Roundup.
* Females fed the maize developed large mammary tumours almost always more often than and before untreated rats used as controls.
The response
* "I do not think the herbicide risks look convincing, especially with respect to cancer." - Thomas Lumley, University of Auckland.
* "I am surprised it was accepted for publication." - David Spiegelhalter, University of Cambridge.
