Patients in Ontario and New Brunswick were given premixed bags that contained too much saline solution, which diluted the chemotherapy agent, Cancer Care Ontario said Tuesday.
Canadian Broadcasting Corp. said the dilutions ranged from three to 20 percent.
Dr. Ken Schneider, chief of oncology at Windsor Regional Hospital, said the impact on patients is likely low.
"It's really the issue of will that particular drug regimen offer the same degree of benefit to the patients that have received it. In that range of approximately 10 percent dose reduction of one of a combination of drugs, the likelihood of any serious outcome in terms of relapses of cancer or poorer outcome than unexpected would likely be small," Schneider said
An outside company, Marchese Health Care supplied the premixed bags, CBC said.
"Our preliminary investigation of this issue leads us to be confident that we have met the quality specifications of the contract we are honoured to have been awarded," the company said in a statement.
Cancer Care Ontario is working with Marchese to identify the cause of the error.