Which threshold for ER positivity? a retrospective study based on 9639 patients

Area of Science:

• Oncology
• Pathology
• Endocrinology

Background:

• Current guidelines suggest estrogen receptor (ER) positivity if ≥1% of tumor cells stain positive by immunohistochemistry.
• Clinical practice often uses a 10% threshold, with limited data on optimal ER positivity thresholds for endocrine therapy efficacy.
• This study investigates differences in patient, tumor, treatment, and survival based on ER-positivity thresholds of 1% and 10%.

Purpose of the Study:

• To compare clinical and pathological characteristics of breast cancer patients based on ER-positivity thresholds of 1% and 10%.
• To evaluate survival outcomes in breast cancer patients across different ER-positivity thresholds.
• To assess the potential benefit of endocrine therapy in patients with low ER positivity (1%-9%).

Main Methods:

• Retrospective analysis of 9639 primary breast carcinoma patients treated between 1990 and 2011.
• Patients categorized into three groups: ER-positive ≥10%, ER-positive 1%-9%, and ER-negative (<1%).
• Comparison of patient demographics, tumor characteristics, treatment, and survival rates among the defined groups.

Main Results:

• 80.5% of tumors were ER-positive ≥10%, 2.6% were ER-positive 1%-9%, and 16.9% were ER-negative.
• Patients with ER-positive 1%-9% tumors were younger and had more advanced disease compared to those with ER-positive ≥10% tumors.
• ER-positive 1%-9% tumors showed worse survival rates than ER-positive ≥10% tumors, and similar survival rates to ER-negative tumors.

Conclusions:

• Tumors with 1%-9% ER positivity exhibit distinct clinical and pathological features compared to those with ≥10% ER positivity.
• Patients with ER-positive 1%-9% disease may not benefit from endocrine therapy, similar to ER-negative cases.
• Further investigation is required to define the clinical benefit of endocrine therapy and molecular subtypes (basal or luminal) in the ER-positive 1%-9% breast cancer group.