Bone-matrix mineralization dampens integrin-mediated mechanosignalling and metastatic progression in breast cancer.

In patients with breast cancer, lower bone mineral density increases the risk of bone metastasis. Although the relationship between bone-matrix mineralization and tumour-cell phenotype in breast cancer is not well understood, mineralization-induced rigidity is thought to drive metastatic progression via increased cell-adhesion forces. Here, by using collagen-based matrices with adjustable intrafibrillar mineralization, we show that, unexpectedly, matrix mineralization dampens integrin-mediated mechanosignalling and induces a less proliferative stem-cell-like phenotype in breast cancer cells. In mice with xenografted decellularized physiological bone matrices seeded with human breast tumour cells, the presence of bone mineral reduced tumour growth and upregulated a gene-expression signature that is associated with longer metastasis-free survival in patients with breast cancer. Our findings suggest that bone-matrix changes in osteogenic niches regulate metastatic progression in breast cancer and that in vitro models of bone metastasis should integrate organic and inorganic matrix components to mimic physiological and pathologic mineralization.

Early Immune Changes Support Signet Ring Cell Dormancy in CDH1-Driven Hereditary Diffuse Gastric Carcinogenesis.

Stage IA gastric adenocarcinoma, characterized by foci of intramucosal signet ring cells (SRC), is found in nearly all asymptomatic patients with germline pathogenic CDH1 variants and hereditary diffuse gastric cancer syndrome (HDGC). The molecular steps involved in initiating malignant transformation and promoting SRC dormancy in HDGC are unknown. Here, whole-exome bulk RNA sequencing (RNA-seq) of SRCs and adjacent non-SRC epithelium (NEP) was performed on laser-capture microdissected (LCM) regions of interest found in risk-reducing total gastrectomy specimens from patients with HDGC (Clinicaltrials.gov ID: NCT03030404). In total, 20 patients (6 male, 14 female) with confirmed HDGC were identified. Analysis of differentially expressed genes (DEG) demonstrated upregulation of certain individual EMT and proliferation genes. However, no oncogenic pathways were found to be upregulated in SRCs. Rather, SRC regions had significant enrichment in pathways involved in T-cell signaling. CIBERSORTx predicted significant increases in the presence of regulatory T cells (Treg) specific to SRC regions. IHC confirmed an increase in FOXP3+ cells in SRC foci, as well as elevations in CD4+ T cells and HLA-DR staining. In summary, the tumor immune microenvironment is microscopically inseparable from stage IA gastric SRCs using a granular isolation technique. An elevation in CD4+ T cells within SRC regions correlates with clinically observed SRC dormancy, while Treg upregulation represents a potential immune escape mechanism. IMPLICATIONS: Characterization of the tumor-immune microenvironment in HDGC underscores the potential for the immune system to shape the transcriptional profile of the earliest tumors, which suggests immune-directed therapy as a potential cancer interception strategy in diffuse-type gastric cancer.