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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.

PURPOSE OF REVIEW: Mucinous ovarian cancers (MOCs) are categorized into infiltrative and expansile subtypes. These subtypes have different characteristics and prognoses. Patients with clinical early-stage disease of both subtypes currently undergo surgical staging (peritoneal washing, biopsies, omentectomy). Peritoneal and lymph node metastases of expansile MOC are rare, but whereas lymph node sampling (LNS) is omitted in these patients, peritoneal staging is not. Therefore, we collected all available MOC data to determine whether staging surgeries could safely be omitted in clinical early-stage expansile and infiltrative MOC.RECENT FINDINGS: Current literature confirms that peritoneal metastases are rare in expansile MOC: more than 90% had early-stage disease. Only 3.4% of the patients with clinical early-stage expansile MOC had positive peritoneal washings at surgical staging. Patients with infiltrative MOC were diagnosed more frequently with advanced-stage disease (21-54%). Moreover, upstaging clinical early-stage infiltrative MOC based on positive cytology, peritoneum and omentum metastases occurred in 10.3% of the patients. Therefore, we recommend that patients with early-stage infiltrative MOC undergo peritoneal staging and LNS. However, in addition to omitting LNS, we can also safely recommend omitting peritoneal staging in patients with early-stage expansile MOC.SUMMARY: Peritoneal metastases are rare in clinical early-stage expansile MOC and peritoneal staging can therefore safely be omitted.