Comprehensive Diagnostic and Therapeutic Approaches for Estrogen Receptor-Low Breast Cancer: A Multidisciplinary Perspective From Oncologists and Pathologists.

This publication addresses estrogen receptor (ER)-low breast cancer, defined by ER expression between 1% and 10%. Biologically, this subtype resembles triple-negative breast cancer (TNBC) more than hormone receptor-positive breast cancer.

There is conflicting evidence regarding the benefit of endocrine therapy (ET) for ER-low breast cancer. However, its response to neoadjuvant chemotherapy and prognosis are similar to those of TNBC.

ER-low breast cancer has largely been excluded from TNBC clinical trials, limiting patient access to novel treatments and relevant data.

Emerging evidence suggests:

• ER-low breast cancer may benefit from immune-chemotherapy regimens similar to TNBC.
• It should be recognized as a distinct, heterogeneous entity requiring dedicated prospective trials.
• Molecular subtyping and immune biomarkers could help tailor treatment and identify patients who might still benefit from endocrine therapy.

The CamE-Lot project uses real-world data and collaboration between pathologists and oncologists to standardize the diagnosis and management of ER-low breast cancer. This effort aims to improve clinical consistency and patient outcomes.