Fennec Pharmaceuticals presented detailed results this week from an investigator-initiated Phase 2 study of its hearing-protection drug PEDMARK in Japanese children and young adults receiving cisplatin chemotherapy, and the numbers support the claim at the center of the drug's existence: hearing can be protected without measurably blunting the chemotherapy. Among 25 patients in the primary efficacy population, 24 percent developed the kind of hearing loss the study was designed to prevent, against a prespecified historical benchmark of 56.4 percent. Tumor responses were observed in 23 of 24 evaluable patients. The two numbers together are the study's argument.
What the 33-patient study was designed to test
The trial, known as STS-J01, enrolled 33 patients across 11 Japanese institutions: 27 children aged 3 to 18 in the primary cohort and 6 infants in an exploratory group. The tumor types were the ones where cisplatin is standard care and hearing loss is a known cost of survival: neuroblastoma, hepatoblastoma, germ cell tumors, bone and soft tissue sarcomas, medulloblastoma, and atypical teratoid rhabdoid tumors. PEDMARK, whose active ingredient is sodium thiosulfate, was given intravenously six hours after each cisplatin infusion, the timing the drug's development program has always treated as essential. Give it too early and the protective agent neutralizes the chemotherapy. The six-hour window is the design.
The efficacy numbers deserve precise treatment, because hearing loss is measured in more than one way and the study reported several. By the ASHA criteria, 24 percent of the primary population developed hearing impairment, against the 56.4 percent benchmark drawn from historical cisplatin-alone data. By the Brock grading system, 84 percent had no hearing loss at all, and there were no Grade 3 or Grade 4 cases. In the largest subgroup, ages 7 to 18, hearing loss occurred in 19 percent by ASHA criteria and 14.3 percent by Brock. The historical comparisons come from the pivotal trials ACCL0431 and SIOPEL-6, where cisplatin-alone arms showed ASHA hearing loss in 56 percent and Brock hearing loss in 63 percent of patients.
The benchmarks the protection is measured against
Those historical trials deserve their place in the argument, because they are the reason the benchmark exists. ACCL0431 and SIOPEL-6 were the randomized studies that established how often cisplatin damages hearing when nothing protects against it, and their numbers, 56 percent and 63 percent, became the reference rates against which every protection strategy is measured. PEDMARK's own approval trials in the United States and Europe ran against those same reference rates, which is why the drug's label rests on the comparison. The Japan study is a smaller, single-arm echo of the same design, and its 24 percent result lands in the same range as the registration trials rather than improving on them. What is new in the Japan data is the combination: hearing protection, tumor responses in 23 of 24 evaluable patients, and pharmacokinetics showing no reduction in cisplatin exposure, all in one dataset presented at once.
An attribution profile with nothing to explain
The safety pattern completes the picture in a way that matters for a supportive-care drug. A drug given alongside chemotherapy competes for attention with the chemotherapy itself, and every adverse event becomes a question of attribution. The study's answer is categorical: across more than 200 treatment-emergent adverse events, none was attributed to PEDMARK, no serious adverse event was attributed to it, and no Grade 4 toxicity of any kind was linked to it. The events that occurred were the expected cisplatin toxicities. For a supportive-care drug, that attribution profile is the product. The drug's job is to reduce one toxicity without adding its own, and the dataset says it did.
The tumor-response number that carries the claim
The antitumor finding is the one that will determine how seriously regulators take the study. Pharmacokinetic analysis showed no reduction in cisplatin exposure, meaning the protective drug did not measurably lower the amount of active chemotherapy in the body, and objective tumor responses were observed in 23 of 24 evaluable patients. The mechanistic explanation the company offers is that by the six-hour mark, cisplatin has already distributed into tumors and begun its antitumor activity, while the remaining circulating platinum is still available to damage the inner ear. The safety profile matched the pattern: across more than 200 treatment-emergent adverse events, none was attributed to PEDMARK and no serious adverse event was attributed to it.
What the Japan data adds to an approved drug
The context for the Japan data is that PEDMARK is already an approved drug in the United States and Europe for preventing cisplatin-induced hearing loss in pediatric patients with localized, non-metastatic solid tumors. The Japan study is not a first proof of concept. It is the data package that could support registration in a market where the drug is not yet approved, and it doubles as a test of the six-hour dosing rationale in a population the drug's label does not yet cover. The 6 infants in the exploratory cohort matter for the same reason: the approved indication has age boundaries, and any future expansion would run through younger patients.
The company's stated next steps are Japan registration and partnership discussions, with full results destined for peer-reviewed publication. Registration in Japan would follow the same logic the drug has used elsewhere: a hearing loss rate of roughly one-quarter against a historical benchmark above half, with tumor response data suggesting the protection did not come at the tumor's expense. Regulators weighing that package will look hardest at the single-arm design. Without a randomized comparison, the historical benchmark carries the statistical weight, and benchmarks can be contested. The study's statistical significance is against a prespecified rate, not against a concurrent control arm.
The study also illustrates a structural feature of this corner of pediatric oncology. Hearing protection trials enroll small numbers because the patient population is small, and the single-arm design with historical controls is often the only feasible one. That makes every trial a negotiation about benchmarks. The 56.4 percent figure comes from real cisplatin-alone cohorts, but trial populations shift over time with changes in supportive care, and a hearing loss rate that looks protective in one era can look like ordinary variation in another. The Japan study's consistency across two grading systems is its best defense against that critique: both measurement schemes point the same direction.
What the study means for patients, stated plainly
For patients and families, the study's meaning is narrower than a press release suggests and still real. A child facing cisplatin for a localized tumor now has, in the United States and Europe, an approved drug that reduces the odds of lifelong hearing loss. In Japan, where PEDMARK is not yet approved, the study is the evidence that could change that. The results do not promise protection for every child. One in four patients in the primary population still developed hearing loss by the study's own measure, and the drug does not address the other toxicities of cisplatin. The honest summary is that the odds moved substantially, and the chemotherapy kept working.
The deeper question the study raises is about the six-hour window itself. If the drug works by mopping up circulating platinum after the tumor has taken what it needs, then the timing is not a convenience but the mechanism, and any real-world use that compresses the window risks both losing the protection and blunting the chemo. That is the operational lesson embedded in the pharmacokinetic data, and it will matter in Japan if registration proceeds. A drug whose efficacy depends on a clock is only as good as the infusion schedules that respect the clock.
The presentation at the SIOP meeting in San Antonio this week puts the data in front of the pediatric oncology community that would have to adopt it, and adoption is the real endpoint. Approval is a regulatory event. Use is a clinical one, and use depends on oncologists accepting that a six-hour post-infusion dose protects hearing without touching tumor response. The Japan study is the clearest single demonstration of that claim yet assembled in one place, and it arrives with registration ambitions attached. Whether it converts into a Japanese approval will test whether the evidence that convinced American and European regulators translates.