Trodelvy, of Gilead Sciences Inc, extended by a month and a half, or 34%, the time that women with advanced stages of a common type of breast cancer lived without their disease getting worse, according to trial data presented Saturday. .
The Phase III study compared Trodelvy with chemotherapy in 543 patients with hormone-sensitive tumors that tested negative for a receptor called HER2 and had stopped responding to at least two previous lines of therapy.
The data, presented in Chicago at the American Society of Clinical Oncology (ASCO) annual meeting, show progression-free survival for the Trodelvy group of 5.5 months compared with 4 months for chemotherapy patients.
“Some will argue whether that is really a clinically significant difference.” Dr. Julie Gralow, ASCO’s medical director, told Reuters. “The real point here is that we have proof of principle that this drug works… I’m sure it will be used.”
Trodelvy, also known as sacituzumab govitecan, uses a tumor-directed antibody to deliver an anticancer drug.
In the first analysis of the study, Trodelvy patients lived a median of 13.9 months, compared with 12.3 months in the chemotherapy group, a difference that was not statistically significant.
“We have to wait for that to mature,” Gilead Chief Executive Daniel O’Day told Reuters. “The final analysis of overall survival will probably be in 2024 … but we’ll see if we analyze it sooner.”
He said Gilead intends to seek US approval based on recent data, pending routine discussions with the Food and Drug Administration.
Patients with HER2-negative, hormone-sensitive metastatic breast cancer are treated with combined endocrine therapy with targeted drugs. As the disease becomes resistant, treatment is limited to chemotherapies with increasingly shorter durations of benefit.
Gilead said in March that the study met its primary goal of reducing the risk of cancer progression or death, but did not disclose any details. Shortly thereafter, the company wrote down $2.7 billion in value from its 2020 acquisition of the drug’s developer, Immunomedics.
“If the data matures and a clearer overall survival benefit emerges, then we think there could be a viable path forward,” BMO Capital Markets analyst Evan Seigerman said in a research note on Saturday.
But he expressed caution about possible competition from Enhertu, an AstraZeneca Plc drug being studied for breast cancer patients with low HER2 levels.
The most common adverse side effects reported by patients with Trodelvy were low white blood cell counts and diarrhea.
Trodelvy is already FDA-approved for previously treated triple-negative metastatic breast cancer and bladder cancer. It is being studied for use in various types of cancer.
O’Day said Gilead hopes to start a trial of Trodelvy as an initial treatment for hormone receptor-positive, HER2-negative breast cancer in the second half of this year.
The drug has a US list price of $2,188 per vial, but Gilead did not provide details on the average dose or duration of treatment.
Wall Street analysts, on average, expect annual sales of the drug to exceed $2 billion by 2026, according to Refinitiv.
(Reporting by Deena Beasley Editing by Bill Berkrot and Lisa Shumaker)