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

Purpose: Many studies report the triple negative breast cancer (TNBC) as the worst subgroup, as such patients do not benefit from anti-hormonal therapy and human epidermal growth factor receptor 2 (HER2) antagonists. While HER2 overexpression was a poor prognostic factor in breast cancer before trastuzumab (Herceptin) was available, TNBC is often reported as the worst BC subgroup since targeted therapy is currently not possible. Since the patience-specific experiences and the current literature did not always align, we aimed to determine the BC subgroup with the shortest survival in our center. Methods: The records of patients with BC who were admitted to Trakya University Faculty of Medicine Department of Medical and Radiation Oncology between July 1999 and December 2019 were reviewed. Patients were divided into four main groups (Luminal A, Luminal B, TNBC, and HER2-enriched) according to the St Gallen International Consensus Panel and four subgroups in accordance with estrogen receptor, progestin receptor and HER2 positivity. Patient characteristics, treatment characteristics and clinical outcomes of the four main subgroups were evaluated. 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. Factors affecting disease-free survival (DFS) and overall survival (OS) were analyzed by Cox regression analysis. Results: Statistical analysis was performed on 2017 patients, after excluding patients with phyllodes tumor, carcinoma-in-situ and missing information from a total of 2474 patients with BC. There were 952 (47.1%) patients in the Luminal A group, 236 (34.1%) in the Luminal B group, 236 (11.7%) in the TNBC group and 142 (7.1%) patients in the HER2 enriched group. HER2-enriched patients had the shortest survival (p < 0.001), with 113.70 ± 7.17 months of DFS and 125.45 ± 3.03 months of OS. For patients who received Herceptin, DFS was 101.50 ± 6.4 months and OS was 118.14 ± 6.16. Patients who did not receive Herceptin had 92.79 ± 18 months of DFS and 94.44 ± 15.23 months of OS. Conclusion: The HER2-enriched subgroup had the worst prognosis despite receiving targeted therapy. While the duration of DFS and OS had no significant difference between TNBC and Luminal A-B subgroups, HER2 enriched subgroup had significantly shorter survival when compared to any other subgroup. HER2-enriched subgroup had a 10-fold greater risk of death compared to the Luminal A subgroup.