Myelophthisis is a form of bone marrow failure due to the substitution of hematopoietic tissue and its stroma by abnormal tissue(. We report a case of a 38-year-old woman under investigation for bicytopenia during maintenance chemotherapy (tamoxifen) for breast cancer (diagnosed 3 years previously). Her physical examination was unremarkable except for pallor. There was no hepatosplenomegaly, lymphadenopathy or breast lesions. Laboratory tests showed normochromic and normocytic anemia (Hb 9.1 g/dL) and thrombocytopenia (117 x 109/L). A peripheral blood smear showed a typical leukoerythroblastic picture. Bone marrow aspiration (with resistance) and biopsy revealed extensive infiltration by breast ductal carcinoma.