Using pan-sarcoma multiomic analysis for identifying sarcoma subtypes with immunogenic potential.
Authors: Lagos Galina , Groisberg Roman , Elliott Andrew , Walker Phillip , Dizon Don S. , von Mehren Margaret , Abraham Jim , Leu Kirsten , DeNardo Bradley , Girda Eugenia , Trent Jonathan C. 
Published: June 2022

11551 Background: Immune checkpoint inhibitors (ICI) have limited efficacy for most sarcomas. Yet, responses are seen in particular sarcoma subtypes, highlighting the need for better predictive biomarkers. The T cell inflamed score (TIS), a gene expression signature reflective of an active tumor immune microenvironment, is associated with ICI response in multiple solid tumors. We evaluated the TIS across a large database of sarcomas to identify which histologic subtypes may benefit from ICI. Methods: Next generation sequencing of DNA (592 gene or whole exome)/RNA (whole transcriptome) was performed for 3605 sarcoma patient samples, representing 45 histologic subtypes (Caris Life Sciences, Phoenix, AZ). TIS (18 gene weighted coefficient composite value; Cristescu 2018) was calculated and the Microenvironment Cell Populations-counter tool (Becht 2016) was used to quantify immune cell populations. Results were compared to melanoma (n = 1255), a representative immunogenic tumor type. High TIS was defined as a score within the upper quartile of melanoma TIS (> 5.5). Percentage with high TIS are reported with 95% CI. Results: Median TIS was highest in inflammatory myofibroblastic tumor (IMT), epithelioid sarcoma (EPIS), myxofibrosarcoma (MFS), well differentiated liposarcoma, and solitary fibrous tumor (SFT). These did not differ significantly from melanoma (p > 0.06). Median TIS was lowest in embryonal rhabdomyosarcoma, desmoid tumor (DES), synovial sarcoma (SYNS), and Ewing sarcoma (ES). Histologic subtypes where > 10% of samples had a high TIS included IMT (29.9% ± 21.7%), MFS (23.3% ± 12.6%), pleomorphic sarcoma (PLSARC) (21.9% ± 5.8%), cutaneous angiosarcoma (ANGS) (18.4% ± 13.9%), spindle cell sarcoma (17.5% ± 7.6%), liposarcoma (LPS) (17% ± 10.7%), EPIS (15.4% ± 19.6%), visceral ANGS (13.2% ± 10.7%), pleomorphic LPS (13.6% ± 14.3%), fibrosarcoma (12.5% ± 13.2%), leiomyosarcoma (11.6%± 3.4%), malignant peripheral nerve sheath tumor (MPNST) (10.2% ± 7.7%), and perivascular epithelioid cell tumor (PEComa) (10% ± 10.7%). The relative abundance of immune and stromal cell populations was highly variable across sarcoma subtypes, yet a strong positive correlation between TIS and immune cell populations was observed for most subtypes (e.g. T cells, Spearman R range: 0.56 [P = 0.08] - 0.96 [P < 0.0001]). A notable exception was SFT, which had a relatively high median TIS but low abundance of CD8+ T cells and B cells. Conclusions: We found high median TIS and/or significant proportions of samples with a high TIS in sarcoma subtypes with previously demonstrated responsiveness to ICI, including MFS, PLSARC, LPS, and ANGS, while unresponsive tumor types such as RMS, DES, SYNS, and ES had low TIS. We further identified subtypes with high TIS but limited prior clinical data supporting ICI use, such as IMT, EPIS, MPNST, SFT, and PEComa. Our results warrant prospective exploration of TIS as a predictive biomarker for ICI use in sarcoma.