To know the prognosis of a patient with cancer allows choosing the most appropriate therapeutic. The expression of the oncogen HER2/neu has been related to an unfavourable prognosis in patients with infiltrating breast carcinoma, for this reason, the purpose of this work was to analyze its predictive and prognostic value in patients with locally advanced breast cancer, treated in the Oncological Institute "Dr Miguel Perez Carreño". Information about personal data of 58 patients was compiled, as well as the received treatment, clinical response data of the biopsy report, histological grade, nuclear grade, node status and evolution of the patient. The determination of the HER2/neu expression was made by inmunohistochemistry, using the avidina-estreptavidin-peroxidasa technique. For the interpretation of the HER2/neu, an agreed score from 0 to 3+ was assigned, using the guidelines of interpretation of the Hercep-Test (DAKO). 37.9% of the cases displayed expression of the HER2/neu in the membrane of the tumour cells. The node state and the hormonal receptors state turned out to be significant to predict the disease-free interval. Patients with strong oncoprotein expression seem to have a quimioresistant tendency to the FAC (5-fluorouracil, doxorubicin and cyclophosphamide) regime. The expression of the HER2/neu receptor is related to a reduction of the disease-free interval and global survival in patients with infiltrating ductal breast carcinoma locally advanced, confirming, in this work, to be a good prognostic factor.