Shielding Sound: Fennec Trial Validates Hearing Protection in Cancer Care

RESEARCH TRIANGLE PARK, N.C. – September 17, 2026 – For decades, pediatric oncologists have navigated a brutal paradox: the very treatments that save a child's life often strip away their ability to hear the world they fought to remain in. Cisplatin, a cornerstone platinum-based chemotherapy, is highly effective against solid tumors but carries a devastating, irreversible side effect. Between 60% and 90% of children treated with the drug suffer permanent high-frequency hearing loss, fundamentally altering their speech development, academic trajectory, and long-term psychological well-being.

Today, the narrative of survivorship is shifting. Fennec Pharmaceuticals has announced compelling detailed results from its Phase 2 STS-J01 clinical trial in Japan, presented at the 58th Annual International Society of Pediatric Oncology (SIOP) Annual Meeting. The data confirms that the company’s flagship therapy, PEDMARK® (sodium thiosulfate injection), significantly reduces the incidence of cisplatin-induced ototoxicity in pediatric and adolescent and young adult (AYA) patients with non-metastatic solid tumors, all without compromising the chemotherapy’s tumor-eradicating power.

For a medical community that has long accepted deafness as the tragic cost of a cure, these findings represent a critical leap forward in prioritizing the quality of life for young cancer survivors.

Decoding the Clinical Impact

The STS-J01 study, an investigator-initiated, open-label trial, enrolled 33 patients across 11 institutions in Japan, primarily within the Japanese Children’s Cancer Group (JCCG). The primary efficacy population consisted of 25 patients between the ages of 3 and 18.

The results were striking. According to American Speech-Language-Hearing Association (ASHA) criteria, hearing loss occurred in only 24.0% of the primary cohort. This represents a statistically significant reduction compared to the prespecified historical benchmark of 56.4%—a control metric drawn directly from the untreated arm of the landmark Children’s Oncology Group (COG) ACCL0431 Phase 3 study.

When evaluated under the Brock grading criteria, the outcomes were equally profound. Fully 84.0% of patients exhibited Grade 0 hearing loss, meaning they retained normal auditory function across all frequencies. Crucially, not a single patient in the trial experienced Grade 3 or Grade 4 severe hearing loss.

“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,” said Eiso Hiyama, M.D., PhD, lead investigator and professor in the Department of Pediatric Surgery at Hiroshima University Hospital. “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.”

The Science of Timing: The Six-Hour Window

Historically, the challenge of administering an otoprotectant alongside chemotherapy has been the risk of "tumor interference." If a drug neutralizes the toxicity of cisplatin in the ear, could it also neutralize its ability to kill cancer cells? This concern previously prompted regulatory caution, limiting the drug's use exclusively to localized, non-metastatic tumors following early survival imbalances in metastatic subgroups in older trials.

The STS-J01 trial directly addresses this through rigorous prospective pharmacokinetic (PK) analyses. The trial achieved an Objective Response Rate (ORR) of 95.8%, with 23 of 24 evaluable patients showing positive tumor responses.

This success hinges on a strict administration protocol: Pedmark is delivered intravenously exactly six hours after the cisplatin infusion concludes.

Independent clinical pharmacologists note that systemic cisplatin rapidly binds to plasma proteins and tumor DNA within the first few hours of administration. By the six-hour mark, the chemotherapy has already initiated its antitumor activity. However, free circulating platinum species slowly permeate the inner ear fluids—the endolymph and perilymph—where they can linger for days, systematically destroying the outer hair cells of the cochlea. Administering sodium thiosulfate at the six-hour threshold allows the compound to chemically neutralize these residual toxins in the bloodstream before they can inflict permanent auditory damage, effectively threading the needle between efficacy and protection.

“The clinical and pharmacologic findings of STS-J01 are compelling,” noted Pierre S. Sayad, PhD, M.S., chief medical officer of Fennec Pharmaceuticals. “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.”

A Blueprint for Asian Expansion

Beyond the clinical triumph, the STS-J01 data serves as the linchpin for Fennec Pharmaceuticals' strategic expansion into the Asian market. Having already secured FDA approval in the United States and European Commission authorization under the brand name PEDMARQSI, the company is actively pursuing registration in Japan.

The Japanese regulatory landscape offers a highly favorable environment for pediatric oncology innovations. Under the Pharmaceuticals and Medical Devices Agency (PMDA), therapies that address severe unmet needs in small patient populations can qualify for Orphan Drug Designation. Industry analysts point out that this designation not only accelerates the review timeline from a standard 12 months down to six to nine months but also grants a lucrative 10-year period of market exclusivity.

Furthermore, Fennec is well-positioned to leverage a regional licensing model. In March 2024, the company executed a blueprint deal with Norgine Pharmaceuticals Ltd. for European and Australasian commercialization, securing a €40 million upfront payment alongside up to €210 million in potential milestones and tiered royalties. Financial experts anticipate Fennec will seek a similar partnership with a domestic Japanese pharmaceutical leader—one with established distribution networks across Japan's specialized university hospital system.

With formulation and method-of-use patents protecting Pedmark until 2039, and a recent patent settlement barring generic entry in the U.S. until at least 2033, Fennec has built a robust intellectual property moat to support its global rollout.

Integrating Innovation into Hospital Workflows

Translating clinical trial success into real-world hospital workflows requires careful logistical management. Because standard pediatric cisplatin protocols often require aggressive inpatient hydration, integrating a 15-minute Pedmark infusion six hours post-chemotherapy fits naturally into existing oncology nursing shifts.

However, the therapy is not without its management needs. Pedmark is formulated as a concentrated sodium salt solution, which can induce transient fluid shifts and electrolyte imbalances. In the STS-J01 trial, the safety profile aligned with known expectations. The primary adverse events were manageable, including hypernatremia and hypokalemia—both common in patients undergoing aggressive hydration combined with cisplatin. Pediatric oncologists routinely manage these risks by adjusting baseline hydration fluids, monitoring serum sodium levels, and providing potassium supplementation and prophylactic antiemetics.

The broader implications of this therapy extend well into the Adolescent and Young Adult (AYA) demographic. The National Comprehensive Cancer Network (NCCN) has already granted Pedmark a 2A endorsement for AYA patients. Emerging data indicates that up to 75% of young adults treated for conditions like germ cell tumors also develop cisplatin-induced ototoxicity, suggesting the addressable market for hearing preservation is expanding as clinicians recognize the lifelong socioeconomic and psychological costs of deafness.

As survival rates for pediatric and AYA solid tumors continue to improve, the definition of successful oncology care is evolving. It is no longer sufficient to simply eradicate the disease; the medical community is increasingly accountable for the condition in which patients are left post-treatment. With the STS-J01 trial validating the safety, efficacy, and precise pharmacological timing of Pedmark, Fennec Pharmaceuticals is proving that the future of cancer care can—and must—include the preservation of a patient's whole life, including their ability to hear it.