Objective: To evaluate the relevance of histological grading (HG) based on core biopsies (CB) for clinical decision making in breast cancer (BC) we evaluated the concordance with HG from surgical specimen (SSP) and the reasons for under-or overgrading. Method: CB and related SSP of 398 BCs were prospectively graded according to the Nottingham grading system (SSP: 65 G1, 162 G2 and 171 G3). CB/SSP agreement rates and positive predictive values (PPV) of CB based HG were calculated. Rates of over-and underestimation of glandular differentiation (GD), nuclear pleomorphism (NP) and mitotic activity (MA) were calculated.