US FDA flagged problems in critical Tavneos trials, leading to Health Canada to advise doctors to halt starting the medication.
The warning issued after the FDA reported data irregularities.
A medical journal has retracted a paper that used the trial data, stating the numbers were unreliable.
The New England Journal of Medicine has also removed pivotal findings from studies connected to Tavneos.
Regulators in both countries are assessing the drug's safety and efficacy.
Amgen has still commented, maintaining the issue unresolved.
The developments spark concerns for patients as of now receiving the treatment.