Abstract 3864: A single-center retrospective study of the immune landscape in patients with untreated liposarcoma (LS) with long-term follow-up

Background: Liposarcoma (LS) is one of the most common soft tissue sarcoma subtypes. The aim of this study was to evaluate the immune landscape along with potential biomarkers in untreated LS tumors from University of Washington (UW) prior to 2018 in relation to patient outcomes. Methods: We performed a retrospective search of UW/Fred Hutchinson Cancer Research Center (FHCRC) CASIS database to identify patients with available untreated formalin fixed paraffin embedded (FFPE) LS tumor samples who were diagnosed prior to 2018. Using the immunoSEQ® Assay (Adaptive Biotechnologies, Seattle, WA), we analyzed the T-cell receptor (TCR) Vβ to describe T-cell repertoire properties. We also used the ImmunoPrism platform (Cofactor Genomics, San Francisco, CA) to quantify the immune cell composition in these tumors. Results: 61 patients with appropriate and available tumors were identified. The median age was 71yrs, and the mean tumor size was 21.18 cm. Tumors were high grade in 34.4% and low grade in 26.2% of cases. Recurrences were seen in 60.7% of patients with a mean recurrence free survival of 41.48 months. 47.5% of patients were alive at the time of our data cutoff with a mean overall survival of 45.83 months. Survival was negatively associated with age and the presence of multiple tumors at the time of surgery. Using the immunoSEQ Assay, we found that the number of infiltrating T cells amongst samples was variable, with a mean T-cell fraction of 9.5% (±11.9). The clonality of the T-cell repertoire was low in most cases, with a mean score of 0.066 (±0.0366). Interestingly, below median T-cell fraction with above median repertoire of clonality together were associated with worse patient outcomes (HR p-value=2.74e-04). Using the ImmunoPrism platform, we found the mean percentage of immune cell subsets in the samples (±std): CD4+ 5.5%(±4.5), CD8+ 7.1% (±10.3), CD19+ 4.7% (±10.4), CD14+ 7.6% (±7.6), CD56+ 5.4% (±4.5), M1 macrophage 0.1% (±0.3), M2 macrophage 2.3% (±1.6), and Treg 4.2 (±6.2%). The mean percentage of immune cells overall was 36.9% (±21.8). Gene expression was statistically lower in patients who recurred before three years: PD-1 (p=0.003), ICOS (p=0.006), BTLA (p=0.033), and CTLA-4 (p=0.018); suggesting a protective effect of a naturally occurring immune response. Further, hierarchical clustering showed the relationship in expression between PD-1, ICOS, BTLA, and ICOS. Variable selection and shrinkage (to account for possible overfitting) using the lasso showed that increased infiltration by CD14+ monocytes and M2-macrophages predicted worse outcomes. Conclusions: LS often has a low T-cell clonality. Low T-cell fraction with high clonality corresponds to worse patient outcomes. Patients with higher expression of PD-1, ICOS, BTLA, and CTLA-4 were more likely to recur after three years vs. patients with lower expression levels. Patients with fewer monocyte and macrophage tumor infiltrates have better outcomes. Citation Format: Brett A. Schroeder, Natalie A. LaFranzo, Bonnie J. LaFleur, Kevin C. Flanagan, Rachel M. Gittelman, Julie Rytlewski, Seth M. Pollack. A single-center retrospective study of the immune landscape in patients with untreated liposarcoma (LS) with long-term follow-up [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3864.