Atezolizumab produced sustained responses in more than a third of patients with alveolar soft part sarcoma in a phase 2 trial.

These results, recently published in The New England Journal of Medicine, supported the US approval of atezolizumab for adults and children aged 2 years or older with unresectable or metastatic alveolar soft part sarcoma.

The trial ( Identifier: NCT03141684) included 52 adult and pediatric patients with alveolar soft part sarcoma. The median age of the adults was 33 years (range, 18 to 70). The 3 pediatric patients were 12 years to 17 years of age.

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Most patients (65%) had undergone prior resection. About half (52%) had received at least 1 line of systemic therapy, and 93% of those patients had received tyrosine kinase inhibitor therapy.

On study, the adults received atezolizumab at 1200 mg once every 21 days. Patients younger than 18 years received atezolizumab at 15 mg/kg of body weight to a maximum of 1200 mg once every 21 days. Patients were treated until disease progression or unacceptable toxicity. Doses could be held for up to 12 weeks for toxicity.

The objective response rate was 37%. One patient had a complete response, and 18 had a partial response. Of the remaining 33 patients, 1 had an unconfirmed partial response, 1 had a partial response according to iRECIST, 28 had stable disease, and 3 had progressive disease.

The median duration of responses was 24.7 months. The researchers noted that 7 of the 52 patients took a treatment break after 2 years of treatment, and their responses were maintained through the data cutoff date.

The median progression-free survival was 20.8 months. The researchers noted, however, that “tumor assessments were performed less frequently in patients who remained in this study for more than 1 year, which potentially affected the assessment of progression-free survival results by 3 to 6 weeks.”

Nearly all patients (96%) had grade 1-2 adverse events (AEs). Grade 3 AEs that were potentially related to treatment occurred in 15% of patients. There were no treatment-related grade 4 or 5 AEs.

Grade 3 treatment-related AEs (each occurring in 1 patient) included anemia, diarrhea, fracture, hyperglycemia, lipase increase, oral mucositis, pain in extremity, pneumonitis, maculopapular rash, serum amylase increase, and vertigo.

“The results of this phase 2 clinical study … support the use of atezolizumab as a safe and effective treatment for advanced [alveolar soft part sarcoma],” the researchers wrote. “Further investigation is needed to inform clinical decisions regarding the duration of atezolizumab treatment, the usefulness and appropriate timing of treatment breaks, and the potential benefit of atezolizumab rechallenge after disease progression.”

Disclosures: This research was partly supported by Genentech. Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of disclosures.


Chen AP, Sharon E, O’Sullivan-Coyne G, et al. Atezolizumab for advanced alveolar soft part sarcoma. N Engl J Med. Published online September 6, 2023. doi:10.1056/NEJMoa2303383