US FDA flagged issues in key 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, stating the numbers were inconsistent.
The New England Journal of Medicine has also removed pivotal results from studies related to Tavneos.
Regulators in both countries are reviewing the drug's safety and efficacy.
Amgen has not yet commented, maintaining the issue unresolved.
The developments spark concerns for patients as of now receiving the treatment.