Acute myeloblastic leukemia cases carrying the translocation t(8;16) (p11;p13) are characterized by the M4 and M5 subtypes, erythrophagocytosis by the blast cells and a poor prognosis, suggesting a new clinical entity. The t(8;16) fuses the MOZ gene which encodes a histone acetyltransferase, located on 8p11 with the CBP gene which also encodes a histone acetyltransferase, located on 16p13, and recent reports suggested that the chimeric transcription MOZ-CBP is essential for leukemogenesis. A 68-year-old woman who had been treated mainly with paclitaxel and carboplatin for preceding ovarian cancer was admitted to our hospital, complaining of right breast mass. She was diagnosed as having breast cancer and acute monocytic leukemia (M5b). Cytogenetic study with spectral karyotyping analysis revealed the development of 47 XX, + 8, t(8;16)(p11;p13). Eleven cases of therapy-related t(8;16) leukemia including the present case have been reported, but prior treatment with paclitaxel and carboplatin-based chemotherapy has never been reported. The relation of histone acetylase and therapy-related leukemia is discussed.