Cyclin-dependent kinase inhibitors 4 and 6 are a new therapeutic class and are indicated for the treatment of postmenopausal hormone-receptor-positive, HER-2-negative, advanced breast cancer. Generally well tolerated, the major side effect is grade 3 neutropenia, which occurs in two-thirds of patients, requiring reduction, spacing out, or even discontinuation of treatment. The study of the physio-pathological mechanism of hematopoietic toxicity, the comparison with homeopathic Materia Medica and our clinical experience enabled us to identify and retain a specific homeopathic therapeutic protocol. The combination of Natrum muriaticum 7c, 3 pills in the morning, Meduloss 8 DH, 15 drops in the afternoon and Silicea 7c, 3 pills in the evening, prescribed as soon as possible and for the whole duration of the treatment, makes it possible to reduce the intensity of neutropenia and concomitant infections. The daily addition of the hetero-isotherapic anti-CDK 4/6 in 7c has sometimes been necessary in cases of persistent neutropenia. Well tolerated by patients and without drug interference, this homeopathic protocol can be prescribed by any doctor. In our experience, homeopathic support treatment makes it possible to avoid the spacing out of sessions, the reduction of dosage, and so represents increased opportunities for the patients. Clinical studies will be needed to verify the favourable clinical results obtained.