Phase 2 trial of atezolizumab for alveolar soft part sarcoma: long-term follow-up

Alveolar soft part sarcoma (ASPS) is a rare cancer with limited treatment options. A phase 2 trial at the National Cancer Institute (53 ASPS patients) found a confirmed objective response rate (ORR) with atezolizumab of 37%, a median duration of response 24.7 months, and a median progression-free survival (mPFS) of 20.8 months. Updated results of the trial with an additional 3 years of follow-up have now been published. The median duration of response increased to 37.0 months. ORR and mPFS remained essentially as previously reported. ASPSCR1::TFE3 fusion type was determine for 47 patients. ORR and mPFS were higher among the 41 patients expressing type 1 than among the six patients expressing type 2. Eleven patients chose a per-protocol drug holiday (range 3.5-26.4 months) after ≥ 2 years of treatment; two experienced disease progression during the holiday. Nine patients elected to receive bevacizumab plus atezolizumab after progressing in monotherapy. ORR was 0% and mPFS was 18.5 months in this cohort. The authors conclude that thes results support the use of atezolizumab for ASPS, even for several years; a drug holiday with careful monitoring may be an option for some patients.