Downregulation of matrix Gla protein is a biomarker for tamoxifen-resistant and radioresistant breast cancer.

Aim: To establish downregulated biomarkers for cross-resistance for radiotherapy (RT) in tamoxifen (TAM)-resistant breast cancer cells. Materials & methods: RNA sequencing was performed on TAM and RT-resistant breast cancer cells. Breast cancer patient cohorts were queried in silico for associations between genes of interest and outcome after TAM treatment or irradiation. Results: 20 genes showed decreased expression in both TAM-resistant and RT-resistant breast cancer cells. Only matrix Gla protein in the primary tumor was associated with outcome after TAM treatment or RT in breast cancer patients. Conclusion: Matrix Gla protein is a biomarker for therapy sensitivity in breast cancer.