Based on expression of ER, PR, HER2, CK5/6, and EGFR, tumor subtypes were immunohistochemically classified as estrogen receptor-positive luminal A (ER+, PR + or PR-, HER2-), estrogen receptor-positive luminal B (ER+, PR + or PR-, HER2+), HER2 overexpression (ER-, PR + or PR-, HER2+), and basal-like (CK5/6+ and/or EGFR+). The gene discussed is ESR1; the disease is neoplasm.