RESEARCH TRIANGLE PARK, N.C. — September 17, 2026

Fennec Pharmaceuticals announced the oral presentation of detailed results from the investigator-initiated Phase 2 STS-J01 study evaluating PEDMARK® (sodium thiosulfate injection) for reducing cisplatin-induced hearing loss in pediatric and adolescent and young adult (AYA) patients with localized solid tumors in Japan. The study met its primary endpoint, with ASHA-defined hearing loss occurring in 24.0% of patients (6/25) compared with a prespecified historical benchmark of 56.4% (P=0.001). The findings were presented at the 58th Annual International Society of Pediatric Oncology (SIOP) Annual Meeting in San Antonio. PEDMARK is the first and only FDA-approved therapy indicated to reduce the risk of cisplatin-associated ototoxicity in pediatric patients 1 month of age and older with localized, non-metastatic solid tumors.

PEDMARK Demonstrates Hearing Protection With No Severe Loss

The STS-J01 results showed clinically meaningful hearing protection alongside the absence of Grade 3 or Grade 4 hearing loss by Brock criteria. Among the 25 patients in the primary efficacy population, 76.0% remained free of ASHA-defined hearing loss, while 84.0% had Grade 0 hearing loss according to Brock grading. No patient experienced Grade 3 or Grade 4 hearing loss. The study enrolled 33 patients across 11 institutions in Japan, including 27 children ages 3 to 18 years in the primary cohort and six patients in exploratory cohorts. PEDMARK was administered intravenously six hours after cisplatin infusion, with dosing adjusted according to body weight. The safety profile remained consistent with the known tolerability of PEDMARK and expected toxicities associated with cisplatin-containing chemotherapy, with no serious adverse event attributed to PEDMARK and no Grade 4 PEDMARK-related toxicity observed.

Pharmacokinetic Data Support Six-Hour Administration Strategy

Prospective pharmacokinetic analyses provided additional mechanistic insight into the six-hour interval between cisplatin and PEDMARK administration. The analyses characterized the interaction between PEDMARK and cisplatin-derived platinum and supported the treatment strategy of administering sodium thiosulfate after sufficient time for cisplatin to distribute and initiate its antitumor activity. Objective tumor responses were observed in 23 of 24 evaluable patients (95.8%), providing clinical context for the delayed administration approach. Fennec said these findings add an independent body of evidence supporting the rationale for separating PEDMARK administration from cisplatin treatment. The STS-J01 study evaluated hearing outcomes using ASHA and Brock criteria while also assessing safety, antitumor efficacy, pharmacokinetics and longitudinal audiometric outcomes, helping expand the evidence base for PEDMARK in pediatric and AYA oncology populations.

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Fennec Advances PEDMARK Registration Strategy in Japan

The STS-J01 findings support Fennec Pharmaceuticals’ efforts to pursue registration of PEDMARK in Japan and explore commercialization opportunities through partnering or licensing. The company is building on evidence from the pivotal Children’s Oncology Group COG Protocol ACCL0431 and SIOPEL 6 Phase 3 studies, which established clinical evidence for PEDMARK’s ability to reduce cisplatin-associated ototoxicity without interfering with antitumor activity. Cisplatin remains an important treatment for multiple solid tumors, but permanent hearing loss can affect speech and language development, education, social development and long-term quality of life, particularly in children. PEDMARK is already FDA approved in the U.S., while the corresponding product PEDMARQSI® is approved in Europe and the U.K. With positive STS-J01 data, pharmacokinetic support for delayed dosing and an established international regulatory foundation, Fennec is continuing to expand the clinical and commercial reach of its ototoxicity-focused portfolio.

Source: Fennec Pharmaceuticals, press release