Abstract P3-05-33: High expression of MiR-99b in breast cancer is associated with cell proliferation signaling and worse patient survivals in breast cancer

Abstract Background: MicroRNA (miR) is single stranded RNA which regulates the gene expression epigenetically by inhibiting the mRNA translation as well as promoting mRNA degradation. MiR-99b is known as a regulator of mechanistic target of rapamycin (mTOR) signaling and was reported as both onco-miR that promote cell proliferation and tumor suppressor-miR in multiple cancers. We hypothesized that there is a complex interaction between miR-99b and cancer signaling pathways as well as tumor microenvironment, which may influence outcomes. Methods: We studied the clinical relevance of miR-99b expression by performing in silico analyses of 1,961 breast cancer patients using two independent large cohorts; METABRIC and TCGA. Results: We found that high miR-99b breast cancer enriched MTORC1 signaling gene set (normalized enrichment score (NES)>1.50 in both cohorts), but not epithelial mesenchymal transition, NF-kB, nor TGF-β signaling gene sets (all false discovery rate (FDR)>0.40). High miR-99b breast cancer was significantly associated with high rates of mutation scores; silent- and non-silent-mutation rate, fraction altered, single-nucleotide variant neoantigens, as well as intratumor heterogeneity and homologous recombination defects. MiR-99b high tumors also enriched several cell proliferation-related gene sets; E2F targets, G2M checkpoint, and Mitotic spindle signaling, and was significantly associated with pathological grade, but not with subtype nor AJCC stage. High miR-99b breast cancer was significantly associated with low fraction of several stromal cells, including adipocytes cells, keratinocytes cells, and lymphatic endothelial cells in tumor microenvironment (all p< 0.001). On the other hand, miR-99b expression was not associated with immune function nor immune cell infiltration in breast cancer, except for dendritic cells (p=0.006 and 0.020, respectively). Finally, breast cancer with high miR-99b expression was significantly associated with worse overall survival (OS) (hazard ratio (HR)=1.23 (p< 0.001) and 1.26 (p=0.027), respectively) and disease-specific survival (DSS) (HR=1.28 (p< 0.001) and 1.39 (p=0.022), respectively), particularly DSS for ER-positive/HER2-negative breast cancer (HR=1.29 (p< 0.001) and 1.82 (p=0.017), respectively), consistently in two cohorts. In conclusion, we found that high miR-99b expressing breast cancer was significantly associated with not only MTORC1 but also cell proliferation and worse patient outcomes particularly in ER-positive/HER2-negative breast cancer. Citation Format: Masanori Oshi, Yoshihisa Tokumaru, Nobuhiko Sugito, Mahato Sasamoto, Rongrong Wu, Li Yan, Akimitsu Yamada, Takashi Ishikawa, Itaru Endo, Kazuaki Takabe. High expression of MiR-99b in breast cancer is associated with cell proliferation signaling and worse patient survivals in breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-05-33.