FDA approves atezolizumab for unresectable or metastatic alveolar soft part sarcoma

On December 9th 2022, The US Food and Drug Administration (FDA) permitted the approval of atezolizumab for adult and pediatric patients 2 years of age and older with unresectable or metastatic alveolar soft part sarcoma (ASPS). 1

ASPS is a rare and highly malignant soft tissue tumor with a high propensity for metastatic spread and resistance to conventional therapies, mostly affecting adolescents and young adults. 2,3 Due to their slow and asymptomatic growth, the majority of ASPS tumors are diagnosed in the advanced stages. Patients with advanced or metastatic ASPS suffer from extremely poor prognosis, with only an estimated 20% of patients still alive at five years, calling for the critical development of novel and effective therapeutic options. 4

The approval of atezolizumab for ASPS followed the results of the Phase II ML39345 (NCT03141684) open-label, single-arm study of 49 adult and pediatric patients with unresectable or metastatic ASPS. Individuals with primary central nervous system (CNS) malignancy or symptomatic CNS metastases, clinically significant liver disease, or a history of idiopathic pulmonary fibrosis, pneumonitis, organizing pneumonia, or active pneumonitis on imaging were excluded.1

The primary endpoint was objective response rate (ORR) and secondary endpoints included duration of response (DOR) and progression-free survival (PFS). ORR was 24% (95% CI: 13, 39). Of the 12 patients who achieved an objective response, 67% had a DoR of at least 6 months, and 42% had a DoR of at least 12 months.1

Adverse events occurred in 41% patients receiving atezolizumab. The most common adverse events included musculoskeletal pain (67%), fatigue (55%), rash (47%), cough (45%), nausea (43%), headache (43%) and hypertension (43%).1

ML39345 is the largest study to date conducted for ASPS, resulting in the first treatment approved for patients with unresectable or metastatic ASPS. The approval of atezolizumab represents a significant success for patients with this extremely rare and historically difficult-to-treat disease. Further trials are currently underway to investigate atezolizumab in combination with other agents for this patient population.

Written by Ellie Jackson


  1. Center for Drug Evaluation and Research. FDA grants approval to atezolizumab for alveolar soft part sarcoma. U.S. Food and Drug Administration. FDA. Available from: https://www.fda.gov/drugs/resources-information-approved-drugs/fda-grants-approval-atezolizumab-alveolar-soft-part-sarcoma
  2. Ferrari A, Brennan B, Casanova M, et al. Pediatric non-rhabdomyosarcoma soft tissue sarcomas: Standard of care and treatment recommendations from the European Paediatric Soft Tissue Sarcoma Study Group (EPSSG). Cancer Management and Research. 2022;Volume 14:2885–902. 
  3. Sarkar P, Mukherjee S, Saha ML, et al. Alveolar soft part sarcoma: A rare diagnosis. Indian Journal of Dermatology. 2013;58(3):244. 
  4. FDA approves Genentech’s Tecentriq as first-ever therapy for a certain advanced rare sarcoma. Genentech: Statements. Available from: https://www.gene.com/media/statements/ps_120922#:~:text=ASPS%20tumors%20can%20grow%20slowly,option%20when%20the%20tumor%20spreads.