Version 1.2022, Endocrine Treatment and Targeted Therapy for Hormone Receptor‐Positive, Human Epidermal Growth Factor Receptor 2‐Negative Metastatic Breast Cancer: ASCO Guideline Update, and 5th ESO‐ESMO International Consensus Guidelines for Advanced Breast Cancer (ABC 5), for patients with HR‐positive/HER2‐negative advanced or metastatic breast cancer, tissue biopsy for PIK3CA mutation testing is indicated when there is disease progression after endocrine‐based therapy [38, 82, 83]. The gene discussed is ERBB2; the disease is breast carcinoma.