Discordance in Immunohistochemistry Results in Breast Pathologies: Effect of Chemotherapy, Specimen Characteristics, or Pathology Center?

Background: Immunohistochemical results are of vital importance in the classification of patients with breast cancer into subgroups and in treatment decision-making at every stage. However, differences can occur in biopsy results obtained from the same patient. In our study, we aimed to investigate the importance of pathological examination, which is a possible reason for the differences in patients’ immunohistochemistry results. Methods: For this purpose, patients were divided into 3 groups. The differences in estrogen receptor, progesterone receptor, HER2, and Ki-67 were examined between the following groups: patients who received neoadjuvant chemotherapy and then underwent surgery (41 patients), patients who underwent surgery without chemotherapy (50 patients), and the same specimen from a different center and our center (21 patients). Results: The pathological discordance rates were 34.1% in the neoadjuvant chemotherapy group, 28% in the surgery without chemotherapy group, and 38.1% in the comparison between our institution and an external center, with no statistically significant difference across the 3 groups ( P = .667). When examining the changes within each group, statistically significant differences were found in HER2 ( P = .002) for the tru-cut biopsy surgery group and Ki-67 ( P = .025) for the group comparing our center to an external center. Conclusions: As a result, it was considered that one of the important reasons for the immunohistochemical differences in breast biopsies, which is a known fact, is the evaluating center and pathologist.