We studied the combined effect of pyrotinib (anti-HER2 drug), tamoxifen (endocrine therapy), and dalpiciclib (CDK4/6 inhibitor) on the HER2+/HR+ breast cancer cell line BT474 to simulate the clinical therapy in MUKDEN 01 trial (Niu et al., 2022). The gene discussed is ERBB2; the disease is breast carcinoma.