The primary tumour of patients with early breast cancer is the main source of information to assess the risk of disease recurrence and to inform the choice of the most appropriate systemic treatment. Accordingly, it is the main responsibility of the pathologists to ensure the patients and treating physicians that all the relevant information is derived from the primary tumour with the highest accuracy and reproducibility. The morphological changes of the tumour cells reflect the aggregate effects of changes occurring in hundreds of genes and may be a very faithful mirror of the biological and clinical behaviour of breast cancer. According to the 2009 St. Gallen Consensus, the systemic therapy of early breast cancer is mainly informed by the expression of hormone receptors and by the HER2 status, and the assessment of Ki67 has been included among the useful parameters to inform the choice of adding chemotherapy to endocrine therapies for patients with ER-positive and HER2-negative disease. A comprehensive approach that includes the accurate evaluation of the morphological features of the tumour, with special reference to the histological type and grade, and the assessment of the main prognostic and predictive parameters (ER, PgR, HER2 and Ki67) should offer to the patients and the treating physicians a robust background upon which the final therapeutic decisions can be safely taken.
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