Phase III PFS Win in Osteosarcoma Masks Missing Survival Safety and Precedent

Ris-Rez Significantly Improves PFS in Relapsed Osteosarcoma Phase III Trial

GSK plc and Hansoh Pharmaceutical Group Co., Ltd. announced positive Phase III ARTEMIS-011 study results in China for risvutatug rezetecan (Ris-Rez) in patients with relapsed osteosarcoma after at least two prior lines of systemic therapy. The trial met its primary endpoint, demonstrating a statistically significant and clinically meaningful improvement in progression-free survival (PFS) compared to chemotherapy. Ris-Rez reduced the risk of disease progression or death by 67% (HR, 0.33; 95% CI, 0.20-0.55; p<0.0001), with a median PFS of 5.5 months versus 1.4 months for chemotherapy. These results were presented at ESMO Congress 2026 and will support a regulatory submission in China.

• Significant Efficacy in Relapsed Osteosarcoma: The ARTEMIS-011 trial demonstrated that Ris-Rez significantly improved progression-free survival (PFS) in patients with relapsed osteosarcoma, reducing the risk of disease progression or death by 67% compared to chemotherapy. Patients treated with Ris-Rez achieved a median PFS of 5.5 months, a substantial improvement over the 1.4 months observed in the chemotherapy arm, with a highly statistically significant p-value of <0.0001.
• Consistent Safety Profile and Regulatory Path: The safety findings for Ris-Rez were consistent with previous studies in this tumor type, with Grade 3 or higher treatment-related adverse events occurring in 93% of Ris-Rez patients (12 mg/kg dose) versus 83% in the chemotherapy arm. These positive results, presented at ESMO 2026, are crucial for Hansoh's upcoming regulatory submission in China, addressing a critical unmet need for patients with limited treatment options.
• Broader Development and Unmet Need: Osteosarcoma is a rare and aggressive cancer primarily affecting children and young adults, with extremely limited treatment options after relapse and progression on prior therapies. The success of ARTEMIS-011 adds to the growing evidence for Ris-Rez across multiple solid tumors and informs GSK's global development program, including ongoing trials in advanced osteosarcoma, soft tissue sarcoma, lung cancer, and prostate cancer, highlighting its potential as a novel B7-H3 targeting ADC.

Why New Options Are Crucial for Relapsed Osteosarcoma

Relapsed osteosarcoma carries a 5-year overall survival (OS) below 30%, with reported 5-year event-free survival (EFS) rates of less than 30% for synchronous or metachronous metastatic or nonresectable primary disease. Complete resection of all tumors is essential for survival, yet resectability is frequently unattainable and standard chemotherapy was insufficiently effective in advanced disease.

• Dependence on complete surgical remission with poor outcomes when resection is incomplete or unfeasible: An incomplete surgical resection (P = 0.02) was associated with an increased risk of death, while complete surgical resection was consistently associated with better outcomes. Patients with unresectable metastases have poor prognosis, with overall survival (OS) of 7.8 months in patients with unresectable metastases compared with 39.6 months in patients with resectable metastases treated with metastasectomy and 20.0 months in patients with resectable metastases who received systemic therapy.

• Uncertain and inconsistent benefit of perioperative and post-relapse chemotherapy: The role of perioperative chemotherapy is uncertain, and results on chemotherapy use were inconsistent. EFS has been rather stable since the introduction of combination chemotherapy including doxorubicin, cisplatin, high-dose methotrexate with leukovorin rescue, and/or ifosfamide.

• Marginal efficacy of salvage regimens: Gemcitabine-docetaxel combination therapy was well tolerated and marginally effective, with overall response rate of 5.6% and disease control rate of 22.3%, median time to progression of 2 months (range: 2-6 months) and overall survival time of 8 months (range: 3-21 months). Adjuvant high-dose thiotepa (HDTp) failed to significantly improve OS and PFS in resectable relapsed osteosarcomas, with two-year OS rate of 66.7% (95% CI 42.5-82.5) for SCT + HDTp versus 50.0% (95% CI 28.2-68.4) for SCT alone, median OS of 27.4 and 24.8 months, respectively (hazard ratio [HR] 0.826, 95% CI 0.393-1.734; p = 0.6123), and median PFS of 15.6 (8.9-24.9) months versus 7.2 (4.8-33.3) months, p = 0.3845.

• Toxicity of intensified approaches and limited durability of repeat surgery: During second high-dose chemotherapy and autologous stem cell transplantation (HDC/ASCT), four patients (36.4%) were treated for severe veno-occlusive disease [VOD], and among four deaths (36.4%), two were due to treatment-related mortality (one veno-occlusive disease [VOD] and one therapy-related myelodysplastic syndrome). After a second pulmonary metastasectomy (PM), the 5-year relapse-free survival and overall survival rates were 27% and 48%, respectively, with interval between the first PM and subsequent detection of pulmonary metastasis (≤12 months) as a poor prognostic factor for both relapse-free survival and overall survival.

• Heterogeneous prognostic landscape with low-quality evidence: Nine prognostic factors were identified: relapse-free interval, site, number and size of lesions, resectability, sex, age, alkaline phosphatase levels and response to chemotherapy. Bilateral lung metastases worsened OS (HR 1.68, 95% CI 1.42-1.99), a relapse-free interval >24 months and complete surgical resection were consistently associated with better outcomes, and substantial heterogeneity and low methodological quality were noted across studies.

ARTEMIS-011: Unpacking Ris-Rez's Positive Phase III Results

Several phase 2 trials have evaluated systemic therapies for relapsed, refractory, or metastatic osteosarcoma using single-arm and randomized designs. Primary endpoints have centered on progression-free survival, clinical benefit, and objective response by RECIST v1.1 or WHO criteria.

• Pazopanib pulmonary metastatic study: single-arm, multicenter, phase 2 study in patients with unresectable, pulmonary metastatic osteosarcoma unresponsive to chemotherapy, excluding prior tyrosine kinase inhibitor therapy; pazopanib at 800 mg once daily for 28-day cycles with tumor responses by local radiology assessment; primary endpoints were progression-free survival at 4 months, concomitant with a demonstrated 30% increase in tumor doubling time relative to pretreatment growth rate.

• OLIE lenvatinib plus ifosfamide and etoposide trial: phase II, open-label, randomized clinical trial in patients aged 2 to 25 years with high-grade osteosarcoma, measurable or evaluable disease per Response Evaluation Criteria in Solid Tumors, version 1.1 (RECIST 1.1), and 1 to 2 prior lines of systemic treatment; lenvatinib (14 mg/m2 taken orally once daily) combined with up to 5 cycles of ifosfamide (3000 mg/m2 intravenously) and etoposide (100 mg/m2 intravenously) on days 1 to 3 of each cycle vs IE alone, with crossover to lenvatinib upon disease progression by independent imaging review; primary end point was progression-free survival (PFS) per RECIST 1.1 by independent imaging review, with secondary end points including PFS rate at 4 months and overall survival.

• Pembrolizumab advanced osteosarcoma trial: single-arm, open-label, phase 2 trial in patients with unresectable, relapsed osteosarcoma; primary endpoint was clinical benefit rate (CBR) at 18 weeks of treatment, defined as complete response, partial response, or stable disease using RECIST v1.1; trial had a Simon´s two-stage design, and ≥ 3 of 12 patients with clinical benefit in stage 1 were required to proceed to stage 2.

• Glembatumumab vedotin AOST1521: phase II study in patients aged ≥12 years and <50 years with relapsed or refractory OS; GV 1.9 mg/kg/dose on day 1 of each 21 day cycle with mandatory pharmacokinetics in patients aged <15 years and gpNMB expression by immunohistochemistry; primary end-point was disease control at 4 months and Response Evaluation Criteria in Solid Tumours response using a 2-stage design.

• Gemcitabine combined with oxaliplatin study: multicentre, non-randomised Phase II study including an osteosarcoma stratum with two-stage Simon design; eligibility included age 6 months to 21 years, measurable, relapsed or refractory solid malignancy, and no more than one previous salvage therapy; gemcitabine 1000 mg/m(2) over 100 min followed by oxaliplatin 100mg/m(2) over 120 min on Day 1 of a 14-d cycle, with tumour response assessed every 4 cycles according to WHO criteria.

Ris-Rez: Expanding Beyond Osteosarcoma in the Pipeline

The knowledge base does not have sufficient information to answer this question.

Ris-Rez: A New Horizon for Relapsed Osteosarcoma in China

The landscape for relapsed osteosarcoma patients has long been bleak, characterized by aggressive disease progression and limited effective treatment options. Conventional chemotherapy regimens, despite various intensification efforts, have historically struggled to deliver meaningful improvements in overall or progression-free survival for these patients (PMID 17227995, 17634494). This grim reality underscores the profound unmet medical need that new therapeutic modalities aim to address.

Against this backdrop, the positive Phase III ARTEMIS-011 study results for Risvutatug rezetecan (Ris-Rez) in China mark a significant turning point. Demonstrating a statistically significant and clinically meaningful improvement in progression-free survival, Ris-Rez reduced the risk of disease progression or death by a remarkable 67%, achieving a median PFS of 5.5 months compared to just 1.4 months for chemotherapy in patients who had already undergone at least two prior lines of systemic therapy. This level of efficacy in a heavily pre-treated population is a substantial clinical achievement, offering a new beacon of hope where few existed.

However, the emerging treatment paradigm for advanced osteosarcoma is becoming increasingly competitive. While Ris-Rez's 5.5-month median PFS is impressive, it is noteworthy that a recent randomized Phase II study of apatinib, a tyrosine kinase inhibitor, in combination with ifosfamide and etoposide, also reported a median PFS of 5.5 months in a similar patient population (PMID 41290609). This suggests that Ris-Rez will need to clearly differentiate itself, perhaps through a superior safety profile, ease of administration, or eventual overall survival benefits, which are not yet reported. The trial's focus on the Chinese market, while strategically important given China's significant research and patient population in bone malignancies (PMID 38552042), also means that global applicability and regulatory pathways in other regions may require further consideration. As the NCCN guidelines continue to evolve with expanded management strategies for recurrent/progressive disease (PMID 42324180), the full safety and long-term survival data for Ris-Rez will be crucial in defining its ultimate role and potential to establish a new standard of care for this challenging disease.