May 31 (Reuters) - Gilead Sciences' ( GILD ) Trodelvy

failed to improve survival for patients with advanced bladder

cancer and only modestly extended the lives of previously

treated patients with late-stage lung cancer in a pair of

clinical trials, raising questions about growth prospects for

the medicine.

Trodelvy has accelerated U.S. approval for treating advanced

urothelial cancer, but Gilead on Thursday said a large trial

failed to confirm that the drug improved survival.

The study also linked Trodelvy to a higher number of deaths

compared to chemotherapy due to side effects including

infection.

On Friday, trial data presented at the American Society of

Clinical Oncology meeting in Chicago showed that Trodelvy

improved survival by just 1.3 months more than chemotherapy for

patients with advanced lung cancer, a difference that was not

statistically significant.

The company in January said that the non-small cell lung

cancer (NSCLC) trial had failed to meet its main goal.

"We believe that Gilead's Trodelvy will likely lose its

FDA-labeled indication for metastatic urothelial carcinoma, or

bladder cancer," Leerink analyst Daina Graybosch said in a

research note on Friday.

The bladder indication is estimated to account for about 10%

of Trodelvy sales, which totaled just over $1 billion in 2023.

Gilead's shares were down 1% at $63.20 on Nasdaq.

Trodelvy, an antibody-drug conjugate, is currently approved

in the U.S. for patients with two specific types of advanced

breast cancer and bladder cancer.

Gilead said the 603-patient lung cancer trial showed a

survival improvement of 3.5 months for patients given Trodelvy

whose tumors had not responded to a last round of immunotherapy.

For patients whose lung cancer had responded to their last

immunotherapy, overall survival was a month longer for the

chemotherapy group.

"We remain cautious on the potential for Gilead to get

Trodelvy on the market in lung cancer based on this study," RBC

Capital Markets analyst Brian Abrahams said in a note on Friday.

Serious side effects were reported by 67% of Trodelvy

patients and 76% of chemotherapy patients. The most common side

effects for Trodelvy were fatigue, diarrhea and hair loss.

Gilead is also studying Trodelvy in combination with Merck's ( MRK )

immunotherapy Keytruda as an initial treatment for

patients with NSCLC, the most common lung cancer.

Results for a small subset of patients in one of those

ongoing studies has shown they lived a median of 13.1 months

before their cancer worsened. That is an improvement over the

seven- to eight-month progression-free survival seen in

Keytruda trials, Bilal Piperdi, Gilead's vice president of

clinical oncology, said.