An extensive gene expression profiling of baseline tumor tissue from patients enrolled in the PALOMA-3 trial, which randomized MBC HR+/HER2- patients with endocrine resistant disease to receive palbociclib + fulvestrant versus fulvestrant alone, showed that among the 50 hallmark gene sets from the Molecular Signatures Database, DDR was among the most significantly involved pathways in resistance to palbociclib [19]. The gene discussed is ERBB2; the disease is neoplasm.