Abstract 2749: The unique tumor immune microenvironment of clear cell ovarian carcinoma

Based on differences in chemosensitivity and clinical outcomes, we hypothesize that clear cell ovarian carcinoma (CCCO) displays a unique tumor immune microenvironment (TIME) compared to high grade serous ovarian carcinoma (HGSOC). Microsatellite instability and ARID1DA mutations are more common in clear cell ovarian carcinoma suggesting improved outcomes with checkpoint blockade immunotherapy use. Our objective is to compare the TIME of CCCO to HGSOC using imaging mass cytometry (IMC). Primary untreated ovarian tumors were collected under an IRB-approved protocol. Formalin fixed paraffin embedded (FFPE) tissue sections were stained with 34 metal-tagged antibodies to detect various cell specific and immune related markers using the Fluidigm protocol. IMC data was obtained by the Fluidigm Helios CyTOF instrument utilizing the Hyperion Imaging System laser ablation module. Images from a 1mm2 area of each tissue section were processed and converted to tiff files using MCD Viewer (Fluidigm). Images were analyzed using a deep learning based data analytic pipeline beginning with cell segmentation then multiple rounds of phenotype clustering for cell type annotation. Various cell phenotypes were then measured for cell density analysis within a tumor enriched area. Spearman correlation was performed between cell densities of CCCO and HGSOC. Samples from 51 patients were used for the study: 10 with CCCO and 41 with HGSOC. In the CCCO group, stage of disease ranged from stage I (70%) to III (10%), but all the HGSOC had stage III (92.7%) or IV (7.3%) disease (p