Extended Immunotherapy Shows Safety Profile in Rare Alveolar Soft Part Sarcoma Beyond Standard Two-Year Treatment
Key Insights
A phase II clinical trial demonstrated that patients with alveolar soft part sarcoma (search) can safely receive atezolizumab immunotherapy beyond the standard two-year treatment period without increased toxicity.
Among 17 patients treated for more than two years, only three experienced moderate-to-severe treatment-related adverse events, all of which were manageable and resolved with dose adjustments or additional medications.
The findings are particularly significant for adolescents and young adults with this ultra-rare cancer (search), who may require extended treatment periods and could live for many years with metastatic disease (search).
Long-term adverse events were rare and manageable among patients with alveolar soft part sarcoma (search) (ASPS (search)) who received immunotherapy beyond the standard two years, according to results from a phase II clinical trial presented at the American Association for Cancer (search) Research (AACR) Annual Meeting 2026 and simultaneously published in the Journal of Clinical Oncology.
The findings address a critical knowledge gap for treating this ultra-rare cancer (search) that primarily affects adolescents and young adults aged 15 to 35, with fewer than 100 people diagnosed annually in the United States.
Clinical Trial Design and Patient Population
As of June 2025, researchers led by Dr. Alice P. Chen from the National Cancer Institute had enrolled 54 patients in the ongoing trial, with atezolizumab response durations ranging between 10 and 69 months. Seventeen patients between ages 11 and 56, with a median age of 29, received treatment for more than two years.
Patients older than 2 received 1,200 mg of atezolizumab every three weeks or a pediatric dose of 15 mg/kg up to 1,200 mg. If disease progressed, adult patients could receive the VEGF (search) inhibitor bevacizumab in combination with atezolizumab. Of the 17 long-term patients, 12 received atezolizumab monotherapy while five received the combination therapy.
Safety Profile and Adverse Events
Among the 17 patients treated beyond two years, only three experienced treatment-related adverse events (TRAEs) that were grade 2 or 3, considered moderate to severe symptoms that are not immediately life-threatening and do not require hospitalization.
The adverse events included:
- One patient receiving atezolizumab plus bevacizumab experienced grade 3 aspartate aminotransferase elevation, indicating potential liver damage
- Another combination therapy patient developed grade 2 hypertension and grade 2 proteinuria, suggesting possible kidney damage
- One patient on atezolizumab monotherapy experienced grade 2 pruritus (itchy skin)
"Among patients who received immunotherapy for longer than two years, we did not observe evidence of increased toxicity and this finding held even among patients treated for more than five years," Chen stated. "This is especially important for adolescents and young adults with ASPS (search), who may live for many years with metastatic disease (search)."
Treatment Management and Resolution
Importantly, none of the atezolizumab-related adverse events resulted in treatment discontinuation, and all symptoms eventually resolved. The pruritus was managed with topical and oral medications, the elevated liver enzyme resolved after bevacizumab dose reduction, and hypertension was controlled with antihypertensive medication.
Clinical Significance for ASPS Treatment
The results are particularly meaningful given the limited treatment options for ASPS (search), a slow-growing cancer (search) that develops in soft tissues and does not respond to chemotherapy. In December 2022, atezolizumab received FDA approval for patients 2 and older with ASPS based on early results from this same trial, where 42% of 49 patients had response durations lasting 12 months or more.
"Because many patients experienced durable responses and remained on immunotherapy for several years, we wanted to understand the potential long-term effects of this treatment, particularly for adolescents and young adults with ASPS (search) who may receive immunotherapy for extended periods," Chen explained.
Unique Safety Profile Compared to Other Cancers
Notably, researchers did not observe the late treatment-related adverse events sometimes seen with long-term immunotherapy use in other cancers, such as lung cancer (search). Chen suggested this difference may relate to the younger patient age or the unique biology of ASPS (search).
"I was pleasantly surprised and happy that these young patients had the opportunity to make independent choices regarding [taking a] drug holiday or continuing treatment," Chen noted.
Study Limitations and Future Directions
The study's limitations include the small patient population, which is inherent to research in ultra-rare cancers. The trial protocol allowed patients to take an atezolizumab drug holiday after two years of progression-free treatment, further reducing the number of patients treated beyond two years.
"Because ASPS (search) is an ultra-rare cancer (search), studies in this population are necessarily small," Chen explained. "For the long-term analysis, these 17 patients provided valuable insight into the safety of long-term atezolizumab therapy."
With atezolizumab approval for ASPS (search) in multiple countries, real-world data will play an important role in understanding the long-term effects of immunotherapy in this patient population. The findings provide crucial information for patients and oncologists regarding treatment management options at the two-year mark.