Multifocal breast cancers are heterogeneous in terms of histologic characteristics and molecular types. In this study, we annotated multiple foci of invasive lesions and ductal carcinoma in situ lesions of 17 cases of multifocal breast cancer and investigated their immunohistochemical phenotypes (estrogen receptor [ER], progesterone receptor [PR], human epidermal growth factor 2 [HER2], and Ki-67 proliferative index). Tumor histologic grade, proliferative index, and phenotypes were varied within each patient. We observed that there were some cases in which the treatment consideration could be changed due to different phenotypes of lesions. The proliferative index tended to be higher in areas where the histologic grade was higher. The triple-negative (TN) type had the highest Ki-67 index, followed by luminal B/HER2-, HER2, luminal B/HER2+, and luminal A types sequentially. As the luminal B lesions comprised a considerable portion of multifocal cancer, we subcategorized them according to several criteria. The proliferation index of the luminal B group was significantly (P < .001) higher in the low hormone receptor (HR) group than in the HR group. When compared by the phenotypes of the surrounding lesions, the proliferative index of luminal B lesions were intimately related to the coexisting phenotypes. In conclusion, the immunohistochemical phenotypes of multifocal breast cancer are heterogeneous, and luminal B type is the commonest of the heterogeneous phenotypes.
Keywords: Breast cancer; Immunohistochemistry; Molecular type; Multifocal; Proliferative index.
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