Two patients with granuloblastic masses of the breast, onsetting at diagnosis and as first relapse site of acute myeloid leukemia are reported. The first case had been diagnosed initially as a carcinoma, and the patient underwent bilateral mastectomy. Acute leukemia was only revealed by histology of the surgical specimen. In the second case a second neoplasia, occurring during acute leukemia, was suspected: a fine needle aspirate of the breast mass showed a leukemic infiltrate. Involvement of breast during acute myeloid leukemia is a rare event and, in our experience, of bad prognostic significance. Mammary glands may be a sanctuary for leukemic cells, contributing to unresponsiveness to chemotherapeutic agents.