In a consequential week for Novartis, the Swiss drug maker released results for two of three trials that Wall Street has watched for in the second half of the year.

Novartis saw U.S.-listed shares soar 6% Tuesday, to $161.25, on positive study data for an experimental treatment for multiple sclerosis called remibrutinib. But the company's announcement of a separate trial failure on Friday-after the market closed ahead of a holiday weekend-was a different story.

A late-stage study of the drug pelacarsen failed to reduce the risk of heart attack and stroke compared to a placebo, Novartis said in a news release.

Chief medical officer Shreeram Aradhye said the study of more than 8,000 trial participants set out to answer "one of the most important unanswered questions in cardiovascular medicine"-essentially, whether lowering lipoprotein(a), which carries cholesterol in the blood, could reduce cardiovascular risk when other big risk factors, such as cholesterol and blood pressure, were also being managed.

The lipoprotein, also referred to as Lp(a), can contribute to plaque building up in the arteries, and a person's levels are mostly determined by genetics. About 20% of the world's population has elevated Lp(a)-a show of the commercial promise for a treatment.

While the study did observe lower levels of Lp(a) with pelacarsen, "the findings did not demonstrate that this translated into reduced cardiovascular risk in the overall study population," Aradhye said.

Amgen is also studying a therapy, olpasiran, aimed at the lipoprotein, which the company described earlier this year as "one of the least understood cardiovascular risk factors."

"The Lp(a) hypothesis is weakened, but not disproven," said Citi analyst Geoff Meacham in a Friday note. He expects pressure on Amgen shares after the Novartis announcement, though he said there are distinctions in the mechanisms between each company's respective drugs, as well as their study participants and endpoints.

For Amgen, "these differences could improve its probability of success, but offer differentiation rather than insulation from the pelacarsen result," Citi said.

Novartis stock fell nearly 5% in after-hours trading Friday. The result could heighten investor focus on an expected readout for a third Novartis investigational drug, del-desiran, which targets a rare neuromuscular disorder called myotonic dystrophy type 1. On its most recent earnings call in July, Novartis said it expected to release data for pelacarsen, remibrutinib and del-desiran "in the coming months."

Goldman Sachs analysts, in a July client note, said Novartis stock was trading at a higher multiple than the sector average, suggesting the price already reflected "success for all three upcoming key read outs, implying there could be greater downside risk, particularly if all three catalysts are not perfect, in our view."

Separately, Novartis confirmed Aug. 31 that it paused trials for an experimental cell therapy known as rap-cel, following three patient deaths, Barron's reported. The news didn't hit shares, as investors' expectations were already more modest.