Prognosis, clinicopathological characteristics, and treatment patterns of patients with ER-intermediate-positive breast cancer undergoing long-term follow-up.

BACKGROUND

Estrogen receptor (ER) expression levels in breast cancer tissue predict the efficacy of endocrine therapy and the prognosis of breast cancer patients. Recently, it was reported that the prognosis of patients with ER-low-positive breast cancer was similar to that of ER-negative patients. This study aimed to investigate how ER expression levels impact the prognosis of patients with human epidermal growth factor receptor 2 (HER2)-negative early breast cancer undergoing long-term follow-up.

PATIENTS AND METHODS

The correlation between ER expression levels and prognosis was retrospectively evaluated in a cohort of 3091 consecutive patients with HER2-negative early breast cancer who were treated at our institute between 1981 and 2022. The median follow-up period was 85.2 (range 0-480) months. The proportion of ER-expressing cells in breast cancer tissues was assessed by immunohistochemistry and used to classify patients into four categories: ER negative (<1%), ER-low positive (1% ≤ ER < 10%), ER-intermediate positive (10% ≤ ER < 2/3), and ER-high positive (≥2/3).

RESULTS

Patients with ER-intermediate-positive breast cancer had a prognosis similar to that of patients with ER-low-positive or ER-negative disease. By contrast, patients with ER-high-positive breast cancer had significantly longer disease-free survival (DFS) and overall survival (OS) times than the other groups. Multivariate analysis demonstrated that ER-intermediate positivity was an independent factor for poor prognosis for both DFS and OS in patients with HER2-negative early breast cancer. The distributions of tumor grades 1, 2, and 3 were nearly equal among the ER-intermediate-positive patients, whereas more than half of patients with ER-high-positive breast cancer had grade 1 tumors. By analyzing changes in prognosis over time, we found that the prognosis of patients with ER-high-positive breast cancer markedly improved over three decades, while that of patients with ER-intermediate-positive disease did not.

CONCLUSIONS

Patients with ER-intermediate-positive breast cancer differ from patients with ER-high-positive breast cancer, suggesting that the treatment of ER-positive breast cancer patients should be tailored based on ER expression levels.