US FDA flagged concerns in critical Tavneos trials, raising Health Canada to advise doctors to stop starting the medication.
The warning issued after the FDA found data problems.
A medical journal has retracted a paper that used the trial data, saying the numbers were inconsistent.
The New England Journal of Medicine has also removed pivotal data from studies connected to Tavneos.
Regulators in both countries are assessing the drug's safety and efficacy.
Amgen has not yet commented, maintaining the issue unresolved.
The developments raise concerns for patients as of now receiving the treatment.