1. 37% of study patients had an objective response to treatment with atezolizumab.
2. Median progression-free survival was 20.8 months.
Evidence Rating Level: 2 (Good)
Study Rundown: Alveolar soft part sarcoma (ASPS) has no standardized therapy and is one of the rarest sarcomas with a low 5-year overall survival. Traditional chemotherapies are generally ineffective; however, recent studies have shown promising outcomes with immune checkpoint inhibitors. This study examined the outcomes of atezolizumab, which binds to programmed cell death-ligand 1 (PD-L1), on objective response and progression-free survival in adult and pediatric patients with ASPS. The primary outcome of this study was an objective response to treatment and secondary outcomes included progression-free survival (PFS) and adverse events (AEs). Additionally, this study explored the possibility that induced expression of absent immune checkpoint factors facilitated the effectiveness of immune checkpoint inhibitors in the treatment of this disease. An objective response to treatment occurred in 37% of the 52 patients, with 35% of patients having a partial response, and 2% of patients with a complete response. The median PFS was 20.8 months. The majority of the 52 patients (50 patients) had a grade 1 or 2 AE; 8 patients had grade 3 AEs. No severe (grade 4 or 5) AEs were reported, and there was no treatment cessation due to AEs. Limitations of this study include that the study population was small, with only 52 patients who received treatment with atezolizumab. Additionally, only one patient with progressive disease had provided a biopsy sample of their tumour (as this was an optional data point). Overall, the results from this study support that treatment of this ultrarare sarcoma may be improved by using atezolizumab.
Relevant Reading: Nivolumab and sunitinib combination in advanced soft tissue sarcomas:
In-Depth [prospective cohort]: This study was a single-group, phase 2 clinical study that enrolled 53 patients aged 2 years and older (52 of whom received treatment) with confirmed ASPS who were anti-PD-1/L1 treatment naïve. Patients were recruited from 17 different sites. 19 of 52 patients had an objective response to atezolizumab (95% confidence interval (CI), 24-51%): a confirmed partial response was observed in 18 patients and only 1 patient had a complete response. There was variable expression of PD-1 and PD-L1. Subgroup results were presented and the partial-response group had 100% of 6 sampled tumours positive for PD-L1 and 83.3% positive for CD3+ lymphocytes (with PD-1 receptor). Additionally, the only PD-L1 negative tumour in this group was noted to become positive later in the study after multiple cycles of treatment. 90% of tumours in the stable-disease group were positive for PD-L1 and 70% of tumours from this group were negative for lymphocytes with PD-1 receptors at baseline (compared to 10% of those in the partial-response group).
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