Five Prime Therapeutics (FPRX) recently presented initial data from a Phase I dose escalation study of FPA150, a first-in-class B7-H4 antibody at ASCO, a conference for the American Society of Clinical Oncology, explains biotech expert John McCamant, editor of The Medical Technology Stock Letter.
While the FPA150 dose-escalation data remain early, in our view, the preliminary signals of activity at low doses, including a confirmed partial response (PR) of 6.2 months in a patient with platinum-resistant ovarian cancer who had been treated with 7 prior lines of therapy shows promise.
Data from the poster included 29 patients with a median of 4 prior treatments and consisted of 12 ovarian, 5 bile-duct/gall bladder, 2 uterine, 2 salivary gland and 8 other cancer.
Efficacy data from the poster highlighted 1 partial response (PR; who subsequently progressed after 6 months), and 8 stable diseases (SD) in 17 patients with high expression of B7-H4 (H-score ≥100), while 10 of the 11 patients with B7-H4 low expression (H-score <50) had progressive disease (PD) and 1 patient had SD.
The next efficacy update is expected at the European Society for Medical Oncology (ESMO) 2019 (09/27-10/01).
While early in development, in our view FPA150 has a significant potential market opportunity as B7-H4 expressing cancers represent a potential $1.7 billion market.
B7-H4 is selectively expressed on multiple solid tumors that have not typically responded to checkpoint inhibitors, including 60% of breast cancer and 50% of ovarian and endometrial cancers.
Biomarker data from the poster were generally consistent with these estimates, with 66% of triple-negative breast cancer (TNBC), 59% of endometrial cancer, 54% of ovarian cancer, and 49% of hormone receptor positive (HR+) breast cancer demonstrating medium to high B7-H4 expression (H-score of 50% or higher).
After the ‘150 update at ESMO, we expect data from FivePrime's partner Bristol-Myers Squibb (BMY) for the Phase III trial the carbo + Opdivo combo in kidney cancer by year end.
