US FDA flagged issues in critical Tavneos trials, causing Health Canada to advise doctors to stop starting the medication.
The warning released after the FDA identified data irregularities.
A medical journal has retracted a paper that used the trial data, saying the numbers were conflicting.
The New England Journal of Medicine has also removed pivotal findings from studies linked to Tavneos.
Regulators in both countries are reviewing the drug's safety and efficacy.
Amgen has so far commented, keeping the issue unresolved.
The developments spark concerns for patients currently receiving the treatment.