Shares of the US drugmaker Pfizer were halted in New York, shortly after 12pm local time.
Trading was stopped after the company announced that it to submit a new drug application to US regulators. Palbociclib is an oreal medication, intended as a treatment for breast cancer.
With traders still waiting on news of a possible takeover of AstraZeneca, some market watchers assumed the halt was related.
The move saw AstraZeneca stock drop by more than one per cent on the FTSE 100. Shares in the UK company have now closed up by more than two per cent higher.
Pfizer trading has now resumed.