A total of 22 TLS cases associated with breast cancer have been reported, including three with hormone therapy only (one with tamoxifen and two with letrozole), three with hormone therapy plus a cyclin-dependent kinase 4/6 inhibitor or PIK3CA inhibitor, two with anti-HER2 therapy, nine with chemotherapy, two with radiation therapy, and three without therapy. This evidence concerns the gene CDK4 and Tumor Lysis Syndrome.