programme for outpatient and medical records was consulted. Data collected for each patient were: sex, age, menopause status, performance status (PS), cancer stage, presence of visceral metastatic disease, therapeutic scheme and number of cycles received. The safety profile was assessed from the number of adverse events (AE), and the severity of AEs was graded on the basis of the common terminology criteria for adverse events, V.5.0. Number of patients and reasons for delays and dose reductions were also determined. Results 34 patients, 100% women, were included, with an average age of 60 (47-81) years, of whom 71% were postmenopausal. 29 patients presented at the beginning of treatment with PS £1. The percentage of patients with metastatic disease was 100%, of whom 76% had visceral metastases. The schemes, average numbers and range of cycles were: palbociclib 125 mg every 3 weeks, 7 (1-17) cycles. 105 AE occurred in 31 patients (91%): 54 haematological, 23 metabolic, 10 digestive, 7 asthenia, 2 cases of infections and 9 other causes. The degree of severity was: anaemia, anorexia asthenia, diarrhoea, dysgeusia, increased levels of GGT/AST/ALT/LDH, mucositis, nausea, neutropenia, itching, palmar-plantar erythrodysaesthesia syndrome, thrombopenia, urticaria and vomiting, grade 1 (59%); anaemia, anorexia, asthenia, headaches, GGT increased, infections, mucositis, nausea, neutropenia and vomiting, grade 2 (30%); and asthenia, neutropenia and GGT increased, grade 3 (12%). There were 13 patients who delayed treatment, and neutropenia was the reason in 85% of patients. 6% of patients had reduced doses of palbociclib because of neutropenia or mucositis. Conclusion and relevance There was a high incidence of AE, the most frequent being grade 1. The most common AE were haematological, with neutropenia being the highest degree. Our studies suggested a high percentage of delays and dose reductions.