On August 18, 2026 858 Therapeutics, a clinical-stage biotechnology company, reported that the U.S. Food and Drug Administration (FDA) has granted Fast Track designation to ETX-19477, the company’s internally discovered PARG inhibitor. The designation has been granted for the treatment of adult patients with BRCA-mutated, hormone receptor positive ("HR+"), human epidermal growth factor receptor 2 negative ("HER2-"), unresectable or metastatic breast cancer.

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"For patients with advanced HR+/HER2- breast cancer, there is an urgent need for new treatment options that can delay disease progression," said Jeffrey Stafford, Ph.D., CEO of 858 Therapeutics. "We are pleased that the FDA has granted Fast Track designation to ETX-19477 and are committed to working closely with the agency to accelerate its development. The designation was supported by preclinical findings and emerging clinical data from our ongoing Phase 1/2 trial, including evidence of antitumor activity."

FDA Fast Track status is designed to facilitate the development and expedite the review of new therapies that are intended to treat serious conditions with unmet medical need. Under the Fast Track designation, the ETX-19477 development program will have access to more frequent interactions with the FDA and may be eligible for accelerated approval and/or priority review if certain criteria are met.

ETX-19477 is being evaluated in an ongoing Phase 1/2, open-label, multicenter study in patients with advanced solid tumors, designed to assess safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary anti-tumor activity. The trial is currently enrolling patients in Phase 2 monotherapy cohorts in BRCA-mutated ovarian cancer and BRCA-mutated HR+/HER2- breast cancer.

About ETX-19477

Poly(ADP-ribose) glycohydrolase (PARG) is an enzyme that catalyzes the removal of poly-ADP-ribose (PAR) chains from proteins during the DNA damage response. PARG inhibition leads to selective cell death in tumors with underlying replication fork defects, including BRCAm tumors, through a mechanism distinct from PARP inhibition. ETX-19477 is an oral, potent, and selective PARG inhibitor that shows robust preclinical activity in mouse models of ovarian, breast, and gastric cancers. 858 Therapeutics is evaluating ETX-19477 in a Phase 1/2 study in patients with advanced solid tumors at multiple sites in the U.S. For more information on the Phase 1/2 study, please visit: View Source

(Press release, 858 Therapeutics, AUG 18, 2026, View Source;Unresectable-or-Metastatic-Breast-Cancer [SID1234670216])