Breast fibroepithelial tumors comprise a heterogeneous spectrum of pathological entities, from benign fibroadenomas to malignant phyllodes tumors. Although MED12 mutations have been frequently found in fibroadenomas and phyllodes tumors, the landscapes of genetic alterations across the fibroepithelial tumor spectrum remain unclear. Here, by performing exome sequencing of 22 phyllodes tumors followed by targeted sequencing of 100 breast fibroepithelial tumors, we observed three distinct somatic mutation patterns. First, we frequently observed MED12 and RARA mutations in both fibroadenomas and phyllodes tumors, emphasizing the importance of these mutations in fibroepithelial tumorigenesis. Second, phyllodes tumors exhibited mutations in FLNA, SETD2 and KMT2D, suggesting a role in driving phyllodes tumor development. Third, borderline and malignant phyllodes tumors harbored additional mutations in cancer-associated genes. RARA mutations exhibited clustering in the portion of the gene encoding the ligand-binding domain, functionally suppressed RARA-mediated transcriptional activation and enhanced RARA interactions with transcriptional co-repressors. This study provides insights into the molecular pathogenesis of breast fibroepithelial tumors, with potential clinical implications.
Trithorax-like group complex containing KDM6A acts antagonistically to Polycomb-repressive complex 2 (PRC2) containing EZH2 in maintaining the dynamics of the repression and activation of gene expression through H3K27 methylation. In urothelial bladder carcinoma, (a H3K27 demethylase) is frequently mutated, but its functional consequences and therapeutic targetability remain unknown. About 70% of mutations resulted in a total loss of expression and a consequent loss of demethylase function in this cancer type. Further transcriptome analysis found multiple deregulated pathways, especially PRC2/EZH2, in -mutated urothelial bladder carcinoma. Chromatin immunoprecipitation sequencing analysis revealed enrichment of H3K27me3 at specific loci in-null cells, including PRC2/EZH2 and their downstream targets. Consequently, we targeted EZH2 (an H3K27 methylase) and demonstrated that -null urothelial bladder carcinoma cell lines were sensitive to EZH2 inhibition. Loss- and gain-of-function assays confirmed that cells with loss of KDM6A are vulnerable to EZH2. IGFBP3, a direct KDM6A/EZH2/H3K27me3 target, was up-regulated by EZH2 inhibition and contributed to the observed EZH2-dependent growth suppression in-null cell lines. EZH2 inhibition delayed tumor onset in -null cells and caused regression of-null bladder tumors in both patient-derived and cell line xenograft models. In summary, our study demonstrates that inactivating mutations of , which are common in urothelial bladder carcinoma, are potentially targetable by inhibiting EZH2.
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