Given that JAM-A has been highlighted as a potential biomarker for worsened prognosis in some cancers [6,12], as well as a potential novel indicator of resistance to HER2-targeted therapies in breast cancer patients [5], it is important that its relevance in this setting is fully elucidated and its intra-tumoral heterogeneity considered as a potential parameter for patient outcomes and response prediction. The gene discussed is ERBB2; the disease is breast cancer.