May 31 (Reuters) - An experimental treatment by Pfizer ( PFE )

and Arvinas ( ARVN ) delayed progression of breast

cancer by more than three months compared to AstraZeneca's ( AZN )

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' ( ARVN ) 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 ) Verzenio, Pfizer's ( PFE ) Ibrance and

Novartis' Kisqali.

Leerink Partners analyst Andrew Berens expects vepdegestrant

to earn $576 million in peak sales in 2032.

Earlier this month, Arvinas ( ARVN ) said that it will not move

forward with two other planned late-stage studies of the drug.