Oct 19 (Reuters) - Gilead Sciences' ( GILD ) Trodelvy

lowered the risk of disease progression in an aggressive type of

breast cancer by 38% when used as an initial treatment,

according to trial results presented on Sunday.

The trial compared Trodelvy to a standard treatment of

chemotherapy in 558 previously untreated patients with advanced

triple-negative breast cancer, or TNBC, whose tumors don't

express the PD-L1 protein - targeted by immune system checkpoint

inhibitors such as Keytruda.

The drug received its first U.S. approval in 2020 for the

treatment of advanced TNBC in patients who had received at least

two prior therapies.

TNBC is an aggressive type of invasive breast cancer that

tends to grow and spread faster, has fewer treatment options and

tends to have a worse prognosis. It accounts for about 10% to

15% of all breast cancers.

Antibody-drug conjugates such as Trodelvy are designed to

deliver an anti-cancer drug more precisely to malignant cells,

causing less damage to healthy cells than chemotherapy.

During the trial, patients on Gilead's drug went for a

median period of 9.7 months without their cancer progressing, a

measure known as progression-free survival, compared to 6.9

months for those on chemotherapy.

The trial's initial results were shared in May. The latest

findings were shared at the European Society for Medical

Oncology meeting in Berlin.

"The ability of sacituzumab govitecan (Trodelvy) to

significantly delay death and progression could represent the

first major treatment advance for this patient population in the

20 years since TNBC was defined," said Javier Cortes, head of

the International Breast Cancer Center in Spain and principal

investigator of the trial.

Gilead noted that overall survival data from the trial was

not yet mature and said it will continue monitoring patient

outcomes through ongoing follow-up and further analysis.

In May, Gilead said Trodelvy in combination with Merck's ( MRK )

blockbuster immunotherapy Keytruda lowered the risk of

TNBC by 35% when used as an initial treatment.