[Changes of HER2 low expression status in primary and recurrent/metastatic breast cancer].

Objective: To investigate the evolution and clinical significance of HER2 low expression status in HER2 negative patients in primary and recurrent/metastatic breast cancers. Methods: The data and archived sections of 259 breast cancer patients with recurrence/metastasis and HER2-negative primary foci were collected from January 2015 to January 2022 at the Fourth Hospital of Hebei Medical University, and the HER2 status of primary and recurrence/metastasis foci was determined by immunohistochemistry (IHC), among which IHC 2+patients were subject to fluorescence in situ hybridization (FISH). The HER2 status was classified as HER2-0 group; patients with IHC 1+, IHC 2+and no FISH amplification were classified as HER2 low expression group; and patients with IHC 3+, IHC 2+and FISH amplified were classified as HER2-positive group. The changes of HER2 status in patients with HER2 low expression in primary versus recurrent/metastatic breast cancer foci were compared, and their clinicopathologic characteristics and prognosis were analyzed. Results: The overall concordance rate between primary and recurrent/metastatic HER2 status in breast cancer was 60.6% (157/259, κ=0.178). A total of 102 patients (102/259, 39.4%) had inconsistent primary and recurrent/metastatic HER2 status; 37 patients (37/259, 14.3%) had HER2-0 at the primary foci and HER2-low expression at the recurrent/metastatic; and 56 patients (56/259, 21.6%) had HER2-low expression in the primary foci and HER2-0 in the recurrent/metastatic. The recurrent/metastatic foci became low-expressing compared with the recurrent/metastatic foci which remained HER2-0 patients, with longer overall survival time, higher ER and PR positivity, lower Ki-67 positivity index, and lower tumor histological grade; all with statistically significant differences (all P<0.05). In the primary HER2-low group, patients with recurrent/metastatic foci became HER2-0 while those with recurrent/metastatic foci remained low expression; there were no statistically significant differences in clinicopathological features and overall survival time (all P>0.05). Conclusions: Unstable HER2 status in patients with HER2-0 and low expression in primary versus recurrent/metastatic breast cancer foci, and HER2-0 in the primary foci but low HER2 expression status in recurrence/metastasis is associated with favourable prognosis, and testing HER2 status in recurrence/metastasis can provide more treatment options for such patients.