Breast Cancer Subtypes and Prognosis: Answers to Subgroup Classification Questions, Identifying the Worst Subgroup in Our Single-Center Series

Abstract Background: Breast cancer (BC) remains the most common cancer in women, and it is the second leading cause of cancer-related death in women. Because of advances in treatment, long life is now possible even in patients with metastatic BC, whereas certain groups of patients survive for a very short time despite being diagnosed at an early stage. In many studies, the triple negative BC subgroup is stated to have the worst prognosis, as such patients are deprived of antihormonal therapy and trastuzumab therapy. While HER2 overexpression was interpreted as a poor prognostic factor before trastuzumab treatment, it was reported to be the worst prognostic subgroup of TNBC in posttrastuzumab publications. In the current study, we aimed to find the worst prognostic subgroup as far as we could by capturing the biodiversity in our series of BC patients, and for this purpose, we compared the treatment results in patients grouped according to their receptor status. Methods: We reviewed the records of patients with BC who were admitted to our department between July 1999 and December 2019. We grouped the patients into four main groups (Luminal A, Luminal B, triple negative, and HER2 enriched) and we recorded patient and treatment characteristics and oncological results. Survival curves were generated using the Kaplan–Meier method, and the significance of survival differences among the selected variables was compared by using the log-rank test. Univariate Cox regression analysis was used to estimate hazard ratios. Then, multivariate Cox regression analysis with the backward elimination method was used to estimate hazard ratios and to identify independent prognostic factors.Results: A total of 2474 patients with BC and after exclusions, statistical analysis was performed on 2017 patients with BC. The HER2 positivity rate was 23.7% and the TNBC patient rate was 11.7% (n = 236). The distribution of the four main groups was 47.1% for Luminal A, 34.1% for Luminal B, 7.1% for HER2 enriched, and 11.7% for the TN subgroup. Age (<35 years); no axillary surgery; Ki67≥15; high tumor grade; high mitotic index; the presence of skin infiltration; advanced T/N stage; the presence of metastasis; nontreatment with chemotherapy; less than 5 years of using TMX or AI; and being in the HER2-enriched subgroup were determined to be negative factors for overall survival as a result of multivariate analysis.Conclusions: The HER2-enriched subgroup had the worst prognosis despite receiving targeted therapy. However, treatment with trastuzumab increased survival 1.5-fold over that of the HER2-enriched subgroup that did not receive it.