Discovering the Similarities and Nuances of ER-low and ER-negative breast cancer.

Abstract

<p>Estrogen receptor (ER) status remains a cornerstone in the classification and management of breast cancer. The traditional dichotomous paradigm of ER-positive versus ER-negative disease is now being challenged by the clinical and biological implications of ER-low (1–10% ER expression) tumors. Emerging evidence will be presented that highlights the similarities and subtle differences between ER-low and ER-negative breast cancers. These features pose unique challenges both to the pathologist and to oncologists due to its intermediate biological behaviour and uncertain response to endocrine therapies. The molecular, immunological, and pathological landscapes of ER-low tumors in comparison to ER-negative tumors that suggest ER-low tumors to be a unique biological subset rather than a mere continuum of ER-positive disease will be considered together with implications for its tumor microenvironment and therapeutic responsiveness. By uncovering the similarities and nuances between ER-low and ER-negative breast cancers, this session aims to enhance understanding and optimize management strategies for this heterogeneous and clinically relevant patient population.</p>