According to American Society of Clinical Oncology (ASCO) recommendations, tumour biomarkers like oestrogen receptor (ER), progesterone receptor (PR) and HER2 expression should be evaluated in primary invasive BC for diagnosis, disease recurrence and especially as a guide for therapy, while increasing levels of CA27.29 or CA15-3 may indicate treatment failure [42]. The gene discussed is ESR1; the disease is breast cancer.