(P 284) THE IMPACT OF SARCOMA SBRT ON THE IMMUNE SYSTEM: EARLY RESULTS FROM A PROSPECTIVE TRIAL

Objective: We sought to prospectively evaluate the baseline immune profile of patients receiving SBRT for metastatic sarcoma and to determine if there is any correlation with survival.

Methods: Patients receive 5 fraction SBRT for metastatic sarcoma. Labs are collected prior to SBRT, after last fraction of SBRT, at 3 to 6 months, and at 1 year or time of progression. Labs consist of CBC, albumin, LDH, CRP, MDSCs and immune and inflammatory panels. High parameter flow analysis was performed. Data was analyzed using FlowJo to visualize clusters of cells at baseline by Uniform Manifold Approximation and Projection (UMAP), FlowSOM, and Marker Enrichment Modeling (MEM). Patients were assessed for local control and survival.

Results: Nine patients with a median age of 23 enrolled on our IRB approved prospective trial. 4 patients have died at a median of 3.25 months post SBRT. Five patients had 1 target treated with SBRT and 4 patients had 2. Targets included lung (6), soft tissue (3), bone (2), and kidney (1). Number of metastases at time of SBRT included 1 (n=2 patients), ≤5 (4), >5-10 (1), >10 (2). 5 patients received concurrent therapy. At time of this analysis, 1 patient had local recurrence, 3 had regional recurrence and 7 had distant failure. Five patients had a complete response to SBRT and 3 had a partial response.
Patients that survived < 6 months had higher frequencies of monocytic MDSC (CD33+HLADR-CD14+) and large granular lymphocytes (CD56+CD16+) at baseline than those that survived >6 months. Patients that survived >6 months had higher frequencies of memory CD4+ T cells and CD57+ T cells at baseline than those that survived < 6 months. There was no significant difference in baseline NTLR, albumin, CRP, or LDH for these small patient groups.

Conclusion: On this trial, patients with metastatic sarcoma had early good responses to SBRT. Patients receiving SBRT for metastatic sarcoma may have different baseline MDSCs, large granular lymphocytes, and memory T cells that relate to survival post SBRT.