Phase Ib Study for the Combination of Doxorubicin, Dacarbazine, and Nivolumab as the Upfront Treatment in Patients With Advanced Leiomyosarcoma: A Study by the Spanish Sarcoma Group (GEIS).

Purpose: Doxorubicin, alongside a select group of cytotoxic agents, is capable of inducing an adaptive immune response via a well-established peculiar type of tumor cell death called immunogenic cell death (ICD). We hypothesize that combining doxorubicin and dacarbazine with nivolumab may enhance therapeutic efficacy by exerting synergy in the ICD circuit. We hereby present a phase Ib trial with this combination.

Patients and methods: Patients with advanced leiomyosarcoma and anthracycline-naïve were eligible. The initial dose level consisted of doxorubicin 75 mg/m² once on day 1, once every three weeks, followed by dacarbazine 400 mg/m² once on days 1 and 2, once every three weeks, plus nivolumab 360 mg once on day 2, once every 3 weeks, for six courses and then 1 year of nivolumab. A (-1) dose level was the same regimen but with nivolumab 240 mg. A classic 3 + 3 phase-I design was used to determine the recommended phase-II dose (RP2D). Secondary end points included overall response rate, safety profile, survival, and translational research.

Results: From January 2002 to July 2023, 24 patients were enrolled and 23 were evaluable for efficacy, excluding one patient because of noncompliant dose. All patients were treated with the initial dose level, then the RP2D. Toxicity was mild, with the most frequent being grade 4 toxicity neutropenia (16.7%) and thrombocytopenia (8.3%), while no grade 5 toxicity occurred. The centrally reviewed objective response rate was as follows: partial response 56.5%, stable disease 39.1%, and progression 4.4%. The 6-month progression-free survival (PFS) rate was 80% (95% CI, 63 to 98). Dynamic increases of HMGB1 in blood significantly correlated with longer PFS.

Conclusion: This scheme of doxorubicin, dacarbazine, and nivolumab is feasible and well tolerated. Clinical activity is encouraging and the prognostic impact of HMGB1 supports the relevance of ICD activation. Further clinical research is already underway with this concept in leiomyosarcoma.