By John Miller

ZURICH (Reuters) – Novartis’s efforts to tackle an elusive gene mutation behind tough-to-treat breast cancer were rewarded on Thursday, as the Swiss drugmaker said one of its investigational medicines slowed disease progression.

Analysts said the drug, called BYL719, is on a trajectory to take a leading role in advanced breast cancer treatment.

Novartis said its drug combined with hormone therapy improved progression-free survival in breast cancer patients whose tumors had hormone receptors but not so-called HER2 proteins.

Specific details of the trial, which compared Novartis’s combination to hormone therapy alone in patients who had failed current treatments, will be released at an upcoming conference, the company said.

The success of BYL719, also called alpelisib, comes after other drugmakers including Roche have seen similar investigational medicines fail.

“We are encouraged by the results observed in the SOLAR-1 study and look forward to submitting the data to an upcoming medical congress and starting discussions with health authorities worldwide,” said Samit Hirawat, the head of Novartis Oncology Global Drug Development, adding this was the first such drug to show not only benefits but also tolerability.

The drug is designed to target a key signaling pathway inside cancer cells, called phosphoinositide 3-kinase, or PI13K, believed to play an important role in some tumors’ development.

In June, Roche abandoned a similar drug, called taselisib, after deciding its modest progression-free survival benefit did not justify side effects that caused nearly a fifth of breast cancer patients getting it to abandon treatment early.

And in July, Novartis unloaded rights to similar molecule, called buparlisib, to China’s Adlai Nortye Biopharma Co Ltd, after doctors concluded it was too dangerous to continue developing in the advanced breast cancer setting, when combined with hormone therapy.

Analysts said Novartis’s trial success with BYL719 means the molecule has the potential to dominate treatment of patients with hormone-receptor positive, HER2-negative breast cancer who failed previous treatments with either hormone therapy or targeted drugs like Pfizer’s Ibrance, Novartis’s recently approved Kisqali or Verzenio from Eli Lilly.

Bruno Bulic, an analyst at Baader Helvea, saw Novartis’s candidate as a potential blockbuster.

“We estimate alpelisib peak sales potential at $1.9 billion, and lift our probability of success to 80 percent,” he said. Bulic has a “buy” rating on Novartis shares, which rose 0.4 percent in early trading.

(Reporting by John Miller; Editing by Michael Shields)