Phase 2 STS-J01 data presented at SIOP 2026 show that Pedmark cut cisplatin-related hearing loss to 24% against a 56.4% historical benchmark, while preserving a 95.8% objective tumor response rate in pediatric and AYA patients.
Fennec Pharmaceuticals presented detailed results from the investigator-initiated Phase 2 STS-J01 clinical trial at the 58th Annual International Society of Pediatric Oncology (SIOP) Annual Meeting in San Antonio, Texas, on Sept 17, 2026, showing that Pedmark (sodium thiosulfate injection) significantly reduced cisplatin-induced hearing loss in pediatric and adolescent and young adult (AYA) patients in Japan without compromising anti-tumor activity.
Primary Endpoint Met
Among 25 patients in the primary efficacy population, ASHA-defined hearing loss occurred in 24% (6/25), significantly below the prespecified historical benchmark of 56.4% (P=0.001), with 76% of patients remaining free of ASHA-defined hearing loss. By Brock criteria, 84% of patients had Grade 0 hearing loss, and no Grade 3 or Grade 4 hearing loss was observed.
The single-arm trial enrolled 33 patients across 11 institutions in Japan — 27 children ages 3–18 years in the primary cohort and 6 patients in exploratory cohorts — all with localized-stage solid tumors, including neuroblastoma, hepatoblastoma, germ cell tumors, bone and soft tissue sarcomas, medulloblastoma, and atypical teratoid rhabdoid tumors. Patients received Pedmark intravenously six hours after cisplatin infusion, with dosing adjusted by body weight.
Tumor Responses and Pharmacokinetic Findings
Objective tumor responses were observed in 23 of 24 evaluable patients (95.8%), and prospective pharmacokinetic analyses provided mechanistic support for the six-hour Pedmark administration interval.
“The clinical and pharmacologic findings of STS-J01 are compelling. We observed a significant reduction in hearing loss, with no Grade 3 or Grade 4 hearing loss by Brock criteria, alongside a 95.8% objective response rate in evaluable patients. The prospective pharmacokinetic analyses further provide important mechanistic insight into why the six-hour interval matters, supporting a model in which Pedmark acts on residual circulating and exchangeable platinum after cisplatin has had time to distribute and initiate its antitumor activity. Together, these findings add an important independent body of evidence supporting the clinical rationale for delayed Pedmark administration,” says Pierre S. Sayad, PhD, MS, chief medical officer of Fennec Pharmaceuticals, in a release.
STS-J01 represents the third study — following the pivotal Children’s Oncology Group (COG) Protocol ACCL0431 and SIOPEL 6 — to demonstrate that Pedmark showed no interference with cisplatin antitumor activity.
Safety Profile
The safety profile was consistent with the known tolerability profile of Pedmark. No serious adverse event was attributed to Pedmark, and no Grade 4 Pedmark-related toxicity was observed.
Clinical Context
Studies show that between 60–90% of patients treated with cisplatin may develop hearing loss, depending on the dose and duration of chemotherapy. Cisplatin-induced ototoxicity can affect speech and language skills, academic performance, social-emotional development, career potential, and the ability to live independently — consequences that can persist long after treatment ends.
“For patients navigating cancer in Japan, the ability to successfully treat their tumors while preserving hearing can have a profound impact on their lives long after treatment ends. Cisplatin remains an important and effective treatment, but the risk of permanent hearing loss represents a significant unmet need, particularly for children and young people who may live with its consequences for the rest of their lives,” says Eiso Hiyama, MD, PhD, lead investigator and professor in the department of pediatric surgery at Hiroshima University Hospital in Hiroshima, Japan, in a release. “The results from STS-J01 are encouraging because they demonstrate significant hearing protection and provide reassuring clinical context regarding antitumor activity with delayed Pedmark administration.”
Japan Registration Plans
Fennec is pursuing registration in Japan and is currently exploring partnering or licensing opportunities for Pedmark. Pedmark received FDA approval in September 2022 and is indicated to reduce the risk of ototoxicity associated with cisplatin in pediatric patients 1 month of age and older with localized, non-metastatic solid tumors. The product is also approved in Europe and the UK under the brand name Pedmarqsi, where it is commercialized by Norgine Pharmaceuticals Ltd.
