الفهرس 
METASTATIC BREAST CANCEROnly 14 pages are availabe for public view
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Abstract
Estrogen receptor (ER) remains the most significant predictive biomarker in breast cancer (BC). ER-low-positive (ER-low) BC is a distinct subgroup, characterized by the expression of ER ranging from 1% to 10% or an Allred score ranging from 3 to 5. Currently, the threshold to determine eligibility for endocrine therapy is 1% ER staining or an Allred score of 3. However, the available data primarily focus on the use of adjuvant endocrine therapy, leaving a significant gap in knowledge regarding metastatic ER-low BC.
Patients and Methods:
This study retrospectively analyzed clinicopathologic characteristics and progression-free survival (PFS) outcome of 41 patients with metastatic ER-low BC. Patients included in the study were diagnosed between 2016 and 2022 with a median follow-up duration of 27 months (range 3- 80 ms).
Results:
Metastatic ER-low BC patients exhibited aggressive characteristics: PR negativity (34%), HER2 positivity (49%), and Ki67 above 20% (54%). Median PFS was 8 months ± 1.6 with a 95% confidence interval (4.87-11.13). Factors that had a statistically significant impact on PFS were: age ≥65 years vs <65 years (3 months vs 9 months, p-value 0.049), cardiovascular comorbidities vs no comorbidities (2 months vs 9 months, p-value <0.001), low PR Allred score (p-value 0.01), Ki67 ≥20% vs <20% (p-value 0.002) and presence of visceral metastases vs non-visceral metastases (6 months vs 24 months, p-value 0.004). Moreover, patients receiving chemotherapy followed by maintenance endocrine therapy as first-line treatment had superior PFS (28 months) compared to chemotherapy or endocrine therapy alone (4 and 7 months, respectively, p-value 0.017). Also, duration of endocrine therapy (≥ 6 months) was associated with better outcomes than primary endocrine resistance (28 months vs 3 months, p-value 0.001). Univariate analysis identified cardiovascular comorbidities (p-value 0.001) and visceral metastases (p-value 0.000) as prognostic factors for shorter PFS. However, multivariate analysis identified visceral metastases (p-value 0.001) only as an independent significant factor for poor PFS.
Conclusion:
Maintenance endocrine treatment after chemotherapy for non-progressing metastatic ER-low BC as first-line results in better PFS. Presence of visceral metastases is a significant factor for prognosis of metastatic ER-low BC.