May 31 (Reuters) - An experimental treatment by Pfizer PFE.N and Arvinas ARVN.O delayed progression of breast cancer by more than three months compared to AstraZeneca's AZN.L Faslodex in patients with a specific gene mutation, according to trial results announced on Saturday.

The findings were presented in Chicago at the annual meeting of the American Society of Clinical Oncology and published in The New England Journal of Medicine.

The trial found the experimental drug vepdegestrant increased survival without progression of the disease in patients with ESR1 mutations by five months, compared to about two months for Faslodex.

The findings followed initial results of the study in March. Those showed the benefit of vepdegestrant in patients with the mutations but failed to show benefit in a larger set of patients, sending Arvinas' shares to a record low.

Saturday's more detailed data showed vepdegestrant increased survival in the larger group of patients by 3.8 months, versus 3.6 months for Faslodex.

The late-stage study enrolled 624 previously treated patients with a type of breast cancer that accounts for nearly 70% of all such cancers.

Erica Hamilton, one of the authors of the study, said that Faslodex "clearly has some challenges now," adding that it is injected into a muscle, versus vepdegestrant's more convenient oral dosing.

Vepdegestrant belongs to a novel class of drugs called PROTAC ER degraders, which are designed to harness the body's natural protein disposal system to specifically target and degrade proteins that spur tumor growth.

Breast cancer accounts for about one-third of all new female cancers each year in the U.S., according to the American Cancer Society.

Approved treatments for this type of advanced breast cancer include Eli Lilly's LLY.N Verzenio, Pfizer's Ibrance and Novartis' NOVN.S Kisqali.

Leerink Partners analyst Andrew Berens expects vepdegestrant to earn $576 million in peak sales in 2032.

Earlier this month, Arvinas said that it will not move forward with two other planned late-stage studies of the drug.

(Reporting by Puyaan Singh in Bengaluru; Editing by Cynthia Osterman)

((Puyaan.Singh@thomsonreuters.com;))