Abstract: Objective：To investigate the intertumoral heterogeneity of multifocal/multicentric breast cancer（MMBC）and its impact on treatment decision.Methods：We retrospectively collected information of 65 cases of patients with multifocal multicentric breast cancer，which included estrogen receptor（ER），progesterone receptor（PR），human epidermal growth factor receptor 2（HER2）and Ki67，and assessed the heterogeneity among the lesions.Molecular phenotype was determined by immunohistochemistry.We also compared the  Intertumoral heterogeneity of molecular type and analyzed its effect on treatment decisions.Results：A total of 65 patients with MMBC were included.Intertumoral heterogeneity in tumor type and grade were detected in 6 of 65 patients（9.2%）and 5 of 65 patients（8.5%）respectively.Intertumoral heterogeneity in ER，PR，HER2，Ki67，molecular type were detected in 5（7.7%），5（7.7%），2（3.1%），6（9.2%）and 10（15.4%）individually.Molecular type of additional lesions in 8 patients（12.3%）can influence the choice of treatment decisions.Conclusion：We conclude that intertumoral heterogeneity of multifocal/multicentric breast cancer was existed in histology and molecular type.Immunohistochemistry tests carried out in all lesions to determine molecular type is necessary for the full treatment of multifocal/multicentric breast cancer.

Key words: breast cancer；multifocal, multicentric, heterogeneity, treatment