ArticleBreast cancer research : BCR2025
Pathological response to pembrolizumab-based neoadjuvant therapy in ER-low vs. ER-zero breast cancer: a Swedish population-based cohort study.
Article in Breast cancer research : BCR, 2025. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 3 papers, 1 of them a synthesis that pooled it.
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3 citing papers in PubMed, 1 synthesis or guideline pooled it.
- Association between endocrine therapy and survival outcomes in estrogen receptor-low breast cancer: a systematic review and meta-analysis.The oncologist · 2026Pooled it
- Characteristics and outcomes of patients with HER2-negative metastatic breast cancers with low expression of estrogen and progesterone receptors in the multicenter ESME cohort.Breast (Edinburgh, Scotland) · 2026Article
- Receptor discordance between primary tumors and nodal metastases and correlation with the 21-gene recurrence score in early-stage, estrogen receptor-positive, node-positive breast cancer.Breast cancer research and treatment · 2026Article
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20 authors.
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Abstract
backgroundEmerging evidence indicates that estrogen receptor-low (ER-low)/human epidermal growth factor receptor 2 negative (HER2-) breast cancer (BC) may more closely resemble ER-negative (ER-zero, < 1%) rather than ER-positive disease in terms of biological and clinicopathological characteristics. In Sweden, ER-low (ER 1–9%) BC is managed as triple-negative breast cancer (TNBC) and is thus eligible for neoadjuvant chemo-immunotherapy. We aimed to investigate real-world pathological response to neoadjuvant pembrolizumab combined with chemotherapy in ER-low versus ER-zero BC patients within a Swedish population-based multi-center cohort.
methodsBC patients with indication to receive neoadjuvant pembrolizumab in combination with chemotherapy in Sweden between 2022 and 2024 were included in the study. Clinicopathological data—including pathological complete response (pCR) status, residual cancer burden (RCB) score, stromal tumor-infiltrating lymphocytes (sTILs) levels, and routine tumor characteristics—were retrieved from laboratory information systems. Associations between categorical variables were assessed using chi-squared (χ2) tests and associations between continuous variables and ER status or pCR were analyzed using Mann–Whitney U-test.
resultsThe total cohort comprised 441 TNBC cases (ER-zero n = 398; ER-low n = 43). In the ER-zero group, the pCR rate and RCB score 0–1 were 50.5% (95% CI: 45.5% to 55.5%) and 60.8% (95% CI: 55.8% to 65.6%), respectively. In the ER-low group, the corresponding values were 58.1% (95% CI: 42.1% to 73%), and 60.5% (95% CI: 44.4% to 75%), respectively. There were no statistically significant differences in either pCR rate (p = 0.46) or dichotomized RCB score (p = 0.88) between the groups. The ER-low group showed significantly higher sTILs percentage compared to the ER-zero group (median sTILs 25% versus 20%, p = 0.046). However, when sTILs were analyzed as a binary categorical variable using a 30% cut-off, no significant difference was observed (p = 0.33).
conclusionsWe observed no significant difference in pathological response to neoadjuvant chemo-immunotherapy with pembrolizumab between ER-zero and ER-low BCs. These findings support previous evidence suggesting that ER-low tumors behave more similarly to ER-zero than ER-positive.
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