Background: RIS is a rare subset of soft tissue sarcoma (STS) with poor prognosis and limited treatment options. We hypothesize that subsets of STS that carry genomic complexity, such as RIS, will have a neoepitope and immune signature that predicts response to immunotherapy as these mutations act as strong antigenic targets for eliciting immune response. Methods: Cases of RIS were identified from an institutional database. Formalin fixed paraffin embedded (FFPE) samples were stained for PD-1, PD-L1, CD3, CD4, CD8. Immune scoring was performed. Tumor-infiltrating lymphocytes (TILs) were assessed using a 4-tiered scale: 0 (no lymphocytes); 1 (1-10/HPF); 2 (11-50/HPF), 3 (51-100/HPF); 4 ( > 100/HPF). TIL staining with PD-1 and PD-L1 was also scored whereby the overall percentage of positive cells on the entire slide was quantified. Tumor DNA was extracted from FFPE samples and underwent whole exome sequencing (WES). Results: FFPE samples from 20 cases of RIS were selected for analysis. PD-1 and PD-L1 expression (threshold set at ≥ 1% positive cells) was seen in 35% and 45% of the cases respectively. CD3⁺, CD4⁺, CD8⁺ T cell infiltration (threshold set ≥ 11 cells /HPF) was seen in 45%, 15% and 20% of cases respectively. 12 exomes of unpaired RIS samples were successfully sequenced. The most common histologies were angiosarcoma (n = 3), undifferentiated spindle cell sarcoma (n = 3), de-differentiated liposarcoma (n = 2) and radiation induced spindle cell sarcoma (n = 2). Provisional analysis did not reveal any pattern to the relative mutational burden between the RIS’s. There does however seem to be relatively higher rate of mutation than that seen in other cancer subtypes. Half the samples had at least one pathogenic or likely pathogenic variant. Different HRAS mutations were seen in two samples (sarcoma NOS and angiosarcoma) and FGFR4 mutation was present in two samples, both spindle cell sarcomas. Conclusions: To our knowledge this is the first study to investigate the immune profile in RIS. Up to 45% of these tumors were positive for PD1/PDL1 expression, as well as presence of tumour infiltrating lymphocytes. Results from WES demonstrate that RIS may benefit from immunotherapy due to a relatively higher mutational burden.