In pre-market trade, shares were up another 0.9% to US$62.65 having already gained the best part of 6% yesterday.
On Monday evening, the drugmaker announced that a combination of its flagship immune-boosting cancer drug Keytruda and an older type of chemotherapy helped newly-diagnosed lung cancer patients live significantly longer in a large trial.
It also said that the cocktail of drugs stopped the disease from advancing.
Analysts praised the ground-breaking result, which came much earlier than expected and would appear to give Merck a sizeable lead over its competitors who are all competing for a piece of the very lucrative pie.
Merck shares took a small beating towards the end of 2017 after it revealed that the results of the chemo-combo trial would potentially be delayed until next year.
That was compounded when rival Roche released initial data in December from its own cancer trial, while any delay would also have given rival Bristol-Myers Squibb & Co (NYSE:BMY) time to produce its own results as well.
As it turns out, Merck knew what it was doing when it decided to look at whether or not the combination treatment could help patients survive – thus taking away a possible advantage of its rivals’ drugs.
Importantly, the combo already has FDA approval in the US so it could start to see an instant jump in sales as doctors take a closer at the treatment.
The results should also help secure European approval after it withdrew its application there last year as regulators asked for more data.