Study Highlights Therapeutic Opportunity for New Breast Cancer Subtype

A study comparing the clinical outcomes of metastatic breast cancer patients with two different subtypes of the disease is published in JAMA Network Open this week, providing insights that could inform treatment selection. The gene ERBB2, also known as HER2, is an established target in breast cancers that overexpress the gene. ERBB2-low breast cancer has been proposed as a subtype for patients with tumors that have an immunohistochemistry assay score of 1+ or 2+ in the absence of ERBB2 amplification. Currently, ERBB2-low patients are not candidates for anti-ERBB2 targeted therapies used in ERBB2-positive patients and little is known about how they respond to conventional therapies, compared to ERBB2-zero patients. To investigate, a team led by scientists from the Institut de Cancérologie de l’Ouest analyzed data on thousands of breast cancer patients with either ERBB2-low or -zero tumors, finding that former had slightly better overall survival than the latter. Rates of progression-free survival under first-line treatment, however, did not differ between the two groups. While correctly identifying ERBB2-low breast cancer remains a challenge, the emergence of promising antibody-drug conjugates suggests there is an opportunity to use ERBB2 as a therapeutic vector in ERBB2-low patients and highlight the relevance of this emerging subtype of breast cancer, the study's authors conclude.