First-line Treatment of Metastatic or Locally Advanced Unresectable Soft Tissue Sarcomas with Conatumumab in Combination with Doxorubicin or Doxorubicin Alone: a Phase I/II Open-label and Double-blind Study

Background: Conatumumab is a fully human monoclonal agonist antibody that binds to death receptor 5 and induces apoptosis in sensitive cells. This study evaluated the safety and efficacy of doxorubicin ± conatumumab as first-line systemic therapy for metastatic or locally advanced/unresectable soft-tissue sarcoma.

Methods: In Phase I, six patients received doxorubicin (75 mg/m2) with conatumumab (15 mg/kg) every 3 weeks. In Phase II, patients were randomised (2:1) to receive doxorubicin with either double-blind conatumumab 15 mg/kg (conatumumab-doxorubicin; n=86) or placebo (placebo-doxorubicin; n=42). Patients who progressed on placebo-doxorubicin could receive open-label conatumumab monotherapy post-chemotherapy (n=21).

Findings: The expected histopathologic subtypes (e.g. leiomyosarcoma, liposarcoma, others) were represented in this trial. No unexpected adverse events were noted in either Phase I or II. Median progression-free survival in Phase II was 5.6 and 6.4 months in the conatumumab-doxorubicin and placebo-doxorubicin arms, respectively (stratified HR: 1.00; p=0.973), with more early progressions noted in the first 3.5 months in the conatumumab-doxorubicin arm. Median overall survival was not reached after 8.6 months median follow-up in either arm. Common adverse events were nausea (conatumumab-doxorubicin: 66%; placebo-doxorubicin: 80%), alopecia (55%; 63%), fatigue (60%; 38%) and neutropenia (32%; 50%). Post-chemotherapy results were not notably improved by conatumumab dosing.

Interpretation: Addition of conatumumab to doxorubicin appeared to be safe but did not improve disease control in a heterogeneous unselected group of patients with soft tissue sarcomas. The results of this trial are very useful for estimating the outcomes of first-line therapy of sarcoma patients treated with standard doxorubicin.