Background: Breast cancer is the cause of considerable morbidity and mortality in women. While estrogen receptor antagonists have been widely used in breast cancer treatment, patients have increasingly shown resistance to these agents and the identification of novel targeted therapies is therefore required. Nemorosone is the major constituent of the floral resin from Clusia Risco and belongs to the class of polycyclic polyisoprenylated benzophenones of the acylphloroglucinol group. The cytotoxicity of nemorosone in human cancer cell lines has been reported in recent years and has been related to estrogen receptors in breast cancer cells.Methods: Changes induced by nemorosone in the cell cycle and gene expression of the MCF-7 BUS (estrogen dependent) breast cancer cell line were analyzed using flow cytometry and the RT2 Profiler PCR array, respectively.Results: In comparison to breast cancer cells without treatment, nemorosone induced discrete cell cycle arrest in the GI phase and significant depletion in the G(2) phase. Moreover, the compound altered the expression of 19 genes related to different pathways, especially the cell cycle, apoptosis and hormone receptors.Conclusion: These promising results justify further studies to clarify mechanisms of action of nemorosone, in view of evaluate the possible use of this benzophenone as adjuvant in the treatment of breast cancer. (C) 2015 Elsevier GmbH. All rights reserved. ; Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) ; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)