US FDA flagged concerns in key Tavneos trials, raising Health Canada to advise doctors to pause starting the medication.
The warning issued after the FDA reported data problems.
A medical journal has withdrawn a paper that used the trial data, saying the numbers were unreliable.
The New England Journal of Medicine has also withdrawn pivotal results from studies linked to Tavneos.
Regulators in both countries are reviewing the drug's safety and efficacy.
Amgen has still commented, leaving the issue unresolved.
The developments raise concerns for patients currently receiving the treatment.