GSK plc filed a Form 6-K on 26 October 2026 disclosing positive Phase III results from the ARTEMIS-011 trial, in which risvutatug rezetecan reduced the risk of disease progression or death by 67% compared with chemotherapy in patients in China with relapsed osteosarcoma.

Key Highlights

  • Primary endpoint met: ARTEMIS-011 demonstrated a statistically significant improvement in progression-free survival (PFS) as assessed by an Independent Review Committee, with a hazard ratio of 0.33 (95% CI, 0.20-0.55; p<0.0001).
  • Median PFS: Patients receiving Ris-Rez remained progression-free for a median of 5.5 months versus 1.4 months with chemotherapy, after a median follow-up of 7.1 months.
  • Safety profile: Grade 3 or higher treatment-related adverse events occurred in 93% of patients receiving Ris-Rez at the 12 mg/kg dose and 83% in those receiving chemotherapy; discontinuation due to TRAEs occurred in 4% of Ris-Rez patients and 2% of chemotherapy patients.
  • Second positive Phase III trial: According to the filing, ARTEMIS-011 is Hansoh Pharmaceutical's second positive Phase III study for Ris-Rez in China.
  • Regulatory submission planned: The results will support a regulatory submission by Hansoh in China, the filing stated.
  • Global rights held by GSK: GSK holds exclusive rights to develop and commercialise Ris-Rez outside mainland China, Hong Kong, Macau, and Taiwan.
  • Breakthrough Therapy Designation: Ris-Rez has received Breakthrough Therapy Designation in the US for relapsed or refractory osteosarcoma, among other regulatory designations, according to the filing.

ARTEMIS-011 Phase III Results and Ris-Rez Development Context

GSK plc (LSE/NYSE:GSK) disclosed that its licensor Hansoh Pharmaceutical Group Co., Ltd. announced positive results from the ARTEMIS-011 study, a multicentre, randomised, open-label Phase III trial evaluating risvutatug rezetecan (Ris-Rez) in patients in China with osteosarcoma who had progressed or relapsed after at least two prior lines of systemic therapy. Patients were randomised 1:1 to receive Ris-Rez 12.0 mg/kg every 3 weeks on day 1, or gemcitabine 1,000 mg/m2 on days 1 and 8 plus docetaxel 75 mg/m2 on day 8 every 3 weeks. The filing noted that the 12 mg/kg dose was selected, versus the 8 mg/kg dose used in the ARTEMIS-008 trial in small-cell lung cancer, to account for potential difficulty in penetrating bone tissue.

The late-breaking results were presented during a Presidential Symposium session at the European Society for Medical Oncology (ESMO) Congress 2026. The filing described osteosarcoma as a rare cancer with a global incidence of approximately 3.4 cases per million people per year, primarily affecting children and young adults, and noted that following progression on two prior lines of treatment, no approved therapies exist. The filing also disclosed that Ris-Rez is an investigational antibody-drug conjugate targeting the B7-H3 protein, which the filing stated is highly expressed in more than 10 solid tumour types.

According to the filing, GSK's global clinical development programme for Ris-Rez includes ongoing Phase III trials in extensive-stage small cell lung cancer and metastatic castration-resistant prostate cancer, as well as the phase Ib/II EMBOLD Sarcoma-202 trial in previously treated unresectable advanced or metastatic sarcomas. The filing stated that more than 1,000 patients have received Ris-Rez as part of GSK's global EMBOLD clinical trial programme. GSK noted in the filing that all forward-looking statements are subject to risks and uncertainties described in its Annual Report on Form 20-F for 2025 and its Q2 Results for 2026.

What Was Disclosed

GSK's Form 6-K for October 2026 reported that the ARTEMIS-011 Phase III trial met its primary endpoint, with Ris-Rez reducing disease progression or death risk by 67% versus chemotherapy in China-based relapsed osteosarcoma patients, with Hansoh planning a regulatory submission in China.