US FDA flagged issues in key Tavneos trials, leading to Health Canada to advise doctors to pause starting the medication.
The warning issued after the FDA identified data issues.
A medical journal has withdrawn a paper that used the trial data, noting the numbers were conflicting.
The New England Journal of Medicine has also removed pivotal data from studies related to Tavneos.
Regulators in both countries are examining the drug's safety and efficacy.
Amgen has not yet commented, keeping the issue unresolved.
The developments spark concerns for patients still receiving the treatment.