Characteristics of HER2-Positive Breast Cancer according to HER2 2+/ Low or 3+/High Classification by Immunohistochemistry Assay: Study of 205 Cases Treated in a Single Center

ABSTRACT

Purpose@#To investigate the characteristics of HER2-positive breast cancer according to HER2 low (2+) or high (3+) classification using immunohistochemistry (IHC). @*Methods@#Data were collected from 205 HER2-positive breast cancer patients in the final assay, regardless of IHC or in situ hybridization (ISH). We thus classified patients into two groups HER2 2+/low and HER2 3+/high based on the IHC assay. We subsequently compared the clinical and pathological characteristics between groups. @*Results@#The median patient age was 49 years in the HER2 2+/low group and 53 years in the HER2 3+/high group. We observed a significantly lower Allred score for estrogen receptor (ER) and progesterone receptor (PR) (0-6) (p<0.001), less lymphatic invasion (LI), (p=0.010), neural invasion (p=0.041), higher Ki-67 (p=0.001), and lower Bcl-2 (p<0.001) in the HER2 3+/high group than in the HER2 2+/low group. Lymph node recurrence was more frequently observed in the HER2 2+/low group than in HER2 3+/high group (p=0.005). Disease-free survival (DFS) was better in the HER2 3+/high group than in the HER2 2+/low group (p=0.028), but there were no significant differences in overall survival between the groups (p=0.233). @*Conclusion@#The HER2 3+/high group was associated with lower ER and PR expression, less LI, higher Ki-67, and lower Bcl-2 than that in HER2 2+/low group in HER2-positive breast cancer. Furthermore, compared to the HER2 2+/low group, the HER2 3+/high group had an improved DFS.