Expression of Breast Cancer Subtypes Based on the Most Important Biomarkers: Comparison of Clinicopathological Factors and Survival

[Background]Breast cancer (BC) is the most common cancer among women worldwide. It can be categorized into at least 5 main groups, based on antibody markers, such as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), which are dissimilar in terms of risk factors, distribution, prognosis, treatment, and clinical outcomes. In this study, we evaluated the survival and therapeutic outcomes of BC using immunohistochemical biomarkers in order to improve disease prognosis and eliminate concerns among women.[Methods]The subjects included 1772 women with a diagnosis of BC from January 1999 to January 2014, admitted to Shohada educational hospital and Azar clinic, Tehran, Iran. In this analytical cross sectional study, we selected a simple classification, based on the expression of ER, PR, and HER2. Then, we classified BC patients into 4 subgroups: luminal A (ER+ and/or PR+, HER2-); luminal B (ER+ and/or PR+, HER2+); basal-like (BCL) (ER-, PR-, HER2-); and HER2/neu (ER-, PR-, HER2+) subtypes. In addition, we integrated lymphovascular invasion (LVI) and tumor grade for identifying the groups in terms of HER2 (1+ or 2+ if LVI- was attributed to luminal A or if LVI+ was attributed to luminal B, respectively). P value ≤ 0.05 was considered statistically significant.[Results]The majority of tumors were luminal A (37.16%), luminal B (15.14%), and BCL (13.12%) subtypes, whereas only 6.82% were related to HER2/neu and others were missing. There was a significant difference between immunohistochemical subgroups with respect to tumor grade (P < 0.001). Grade 2 was more frequent among luminal A and B subtypes, while grade 3 was more common among BCC and HER2-like subtypes, respectively. In the comparison of hazard ratio (HR) in each group, luminal B subtype was significantly more frequent than luminal A in HER2/neu. Therefore, HR of luminal A, HER2/neu, and luminal B subtypes was 1, 3.5, and nearly 2, respectively (P < 0.001); in fact, risk of HER2/neu was 3.5 times higher than that of luminal A.[Conclusions]These findings indicate that risk of mortality in each subgroup can be reduced by adjusting for tumor grade and stage.