Thirty-seven patients with breast tumors in stage III and IV were selected, and a new method to remove fragments of tissue for anatomopathologic study was used. The "punch" of Keyes was introduced towards the tumor, under strong pressure, with clockwise and counter-clockwise rotational movements. In thirty-eight biopsies, the anatomopathologic study allowed the authors to make a perfect evaluation of the structure, and the diagnosis made was of infiltrating carcinoma of the breast. This method proved to be a quick, safe and simple procedure, free of complications, and it allows for anatomopathologic diagnosis in 100% of the cases.