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Objective: Mucinous ovarian carcinoma (MOC) is a rare histotype of ovarian cancer, with low response rates to standard chemotherapy, and very poor survival for patients diagnosed at advanced stage. There is a limited understanding of the MOC immune landscape, and consequently whether immune checkpoint inhibitors could be considered for a subset of patients., Methods: We performed multicolor immunohistochemistry (IHC) and immunofluorescence (IF) on tissue microarrays in a cohort of 126 MOC patients. Cell densities were calculated in the epithelial and stromal components for tumor-associated macrophages (CD68+/PD-L1+, CD68+/PD-L1-), T cells (CD3+/CD8-, CD3+/CD8+), putative T-regulatory cells (Tregs, FOXP3+), B cells (CD20+/CD79A+), plasma cells (CD20-/CD79a+), and PD-L1+ and PD-1+ cells, and compared these values with clinical factors. Univariate and multivariable Cox Proportional Hazards assessed overall survival. Unsupervised k-means clustering identified patient subsets with common patterns of immune cell infiltration., Results: Mean densities of PD1+ cells, PD-L1- macrophages, CD4+ and CD8+ T cells, and FOXP3+ Tregs were higher in the stroma compared to the epithelium. Tumors from advanced (Stage III/IV) MOC had greater epithelial infiltration of PD-L1- macrophages, and fewer PD-L1+ macrophages compared with Stage I/II cancers (p = 0.004 and p = 0.014 respectively). Patients with high epithelial density of FOXP3+ cells, CD8+/FOXP3+ cells, or PD-L1- macrophages, had poorer survival, and high epithelial CD79a + plasma cells conferred better survival, all upon univariate analysis only. Clustering showed that most MOC (86%) had an immune depleted (cold) phenotype, with only a small proportion (11/76,14%) considered immune inflamed (hot) based on T cell and PD-L1 infiltrates., Conclusion: In summary, MOCs are mostly immunogenically 'cold', suggesting they may have limited response to current immunotherapies., Competing Interests: Declaration of Competing Interest NSM has received a travel grant from NanoString technologies, unrelated to this work. DDLB has received research support grants from Roche-Genentech, AstraZeneca, and BeiGene (paid to institution); and personal consulting fees from Exo Therapeutics, that are outside the submitted work. MF has participated in Advisory Boards/Consulting from Astra Zeneca, Novartis, GSK, Takeda, Lilly, MSD Eisei and received honoraria/speakers' fees from AstraZeneca, GSK, ACT-Genomics; Research funding to institution: from AstraZeneca, Novartis, Beigene, all unrelated to this work. ADeF has received funding from AstraZeneca, unrelated this work. NS has received honoraria for invited participation in advisory boards hosted by Astra-Zeneca-MSD and Glaxo SmithKline, unrelated to this work. UM had stock ownership in Abcodia until October 2021, and UCL had a license agreement (2011–2021) with Abcodia not related to this work. BHN is a co-founder of Innovakine Therapeutics Inc., unrelated to this work., (Copyright © 2022 The Author(s). Published by Elsevier Inc. All rights reserved.)

Objective: Advanced stage mucinous ovarian cancers are diagnostically and therapeutically challenging. Histotype specific trials have failed due to low recruitment after excluding non-ovarian primaries. Mucinous ovarian cancers are commonly metastatic from other sites however lack definitive diagnostic markers. We suggest a classification of mucinous ovarian cancers of uncertain primary origin 'MO-CUPs' in clinical trials. This study aims to identify drug targets to guide treatment and future trials., Methods: We analyzed a large de-identified, multi-platform tumor profiling dataset of MO-CUPs enriched for advanced stage and recurrent cases submitted to Caris Life Sciences. Available data included a 45-gene next-generation sequencing (NGS) panel, gene amplification of HER2 and cMET and 18 immunohistochemical (IHC) markers of drug sensitivity/resistance., Results: Mucinous tumors from 333 patients were analyzed, including 38 borderline tumors and 295 invasive cancers. The most common mutations in a subset (n = 128) of invasive cancers were KRAS (60%), TP53 (38%), PIK3CA (13%) and PTEN (9%). Borderline tumors had higher rates of BRAF mutations, and PGP and TOP2A overexpression than invasive cases. KRAS mutant invasive cancers had lower expression of thymidylate synthase (p = 0.01) and higher expression of TUBB3 (p = 0.01) than KRAS wildtype tumors., Conclusions: To our knowledge, this is the largest series profiling mucinous ovarian cancers and almost certainly includes cases of ovarian and non-ovarian origin. Given the difficulty recruiting patients to histotype-specific trials in rare subsets of ovarian cancer, it may be more important to focus on identifying potential treatment targets and to personalise treatment and design clinical trials in MO-CUPS agnostic of primary site to overcome these issues., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)