Development and validation of multivariate predictors of primary endocrine resistance to tamoxifen and aromatase inhibitors in luminal breast cancer reveal drug-specific differences [HumanMethylationEPICv2]

In the WSG-ADAPT trial (NCT01779206), HR+/HER2-EBC patients underwent pre-operative short-term endocrine therapy (pET). Treatment response was determined by immunohistochemical in-situ labeling of cycling cells (G1 to M-phase) with Ki67 before and after pET. We performed Infinium MethylationEPICv2-based DNA methylation analysis post-pET in a validation cohort2 (n=176, unmatched). Predictive indices of endocrine resistance under both treatments were calculated. DNA was submitted for DNA methylation analysis using HumanMethylationEPICv2 (EPICv2) BeadChips (Illumina, CA, USA), including an additional restore step for FFPE material.