Hsa-miR-155-5p expression in primary breast tissue may have the potential for prediction of breast cancer brain recurrence: results from the multi-institutional exploratory cohort study

Abstract Background Despite the known incidence of brain metastases in breast cancer, no useful biomarker has been clinically established for breast cancer brain metastasis (BCBM). In the present study, we aimed to examine the expression of microRNAs (miRNAs) related to BCBM in formalin-fixed paraffin-embedded (FFPE) tissues to identify their usefulness as predictive biomarkers of breast cancer brain recurrence (BCBR). Methods Pairs of primary breast and metastatic site tissue samples were collected from 38 patients who experienced the first recurrence of metastasis to a single distant organ (brain/lungs/liver/bones = 11/12/9/6 patients) between January 2007 and December 2021 at five institutions in Japan. We evaluated the expression of 15 miRNAs in FFPE specimens of untreated breast and metastatic sites from the same patient using quantitative polymerase chain reaction. Results Analysis of the selected 15 miRNAs revealed that hsa-miR-155-5p exhibited significant BCBR-specific overexpression in untreated primary breast tissues (p