Studies have additionally highlighted conversion between HER2-low subtype and HER2-enriched subtype, with the latter identified in brain metastasis (Turner et al., 2021); and patients with luminal A subtypes that differentiate into HER2-enriched metastatic cancer but remain unresponsive to therapy (Garcia-Recio et al., 2020). The gene discussed is ERBB2; the disease is metastatic malignant neoplasm.