tumor downsizing prior the ICI treatment might improve outcome

[Olga]

The article is about the melanoma patients, but there is no reason to expect that it might be different in ASPS.

Response of patients with melanoma to immune checkpoint blockade - insights gleaned from analysis of a new mathematical mechanistic model.
https://www.ncbi.nlm.nih.gov/pubmed/31580835

"Importantly, the initial tumor burden influences the response to treatment: small tumors respond better to treatment than larger tumors. "
If there is a large unresected primary tumor or metastasis, you might want to consider some de-bulking or removal of at least larger tumors prior to starting the systemic treatment as they might suppress the immune system ability to respond after the breaks are removed by the ICI drugs. Complete recovery after the surgery would be also beneficial from the same point of view.