Background and importance Due to its recent commercialisation, the safety profile of palbociclib is undergoing special surveillance. Tolerability and safety problems often lead to dose reductions, introduction of supportive treatment or even treatment discontinuation.

Aim and objectives To evaluate the safety and tolerability of palbociclib in clinical practice in a third level hospital.

Material and methods This was retrospective cohort study. Inclusion criteria were all patients who started treatment with palbociclib between 1 January 2019 and 31 August 2019. Toxicity level was classified according to CTCAE V.5.0. Demographic and clinical data were collected from the patient electronic medical records.

Results Forty patients were included (n=40), all women, with a median age of 60 years (range 34–88). All had an ECOG performance status of 0–1 at the time of initiation of palbociclib. Ten patients received palbociclib in combination with fulvestrant and 30 in combination with an aromatase inhibitor. The median number of cycles received was 4 (1–8).

Haematological toxicities detected were grade 1–2 neutropenia (30% of patients), grade 3–4 neutropenia (47%), thrombocytopenia (37%), anaemia (45%), lymphopenia (7%) and leucopenia (35%). No patient suffered from febrile neutropenia. The incidence of infections during treatment was 5%. Other non-haematological adverse events detected with an incidence >5% included asthenia (15%), nausea (15%) and hypertransaminasaemia (7%).

Toxicity led to delay or temporary interruption of treatment in 50% of patients (median 1 interruptions/delays of treatment, range 1–3). Dose reduction to 100 mg was required in 22.5% of patients. No patient required a second reduction in dose. Three patients (7.5%) required administration of G-CSF as supportive therapy. Only one patient had to stop treatment permanently due to toxicity.

Conclusion and relevance Our population showed mainly haematological toxicities, with an incidence of neutropenia similar to clinical trials. However, the incidence of infections and non-haematological toxicities was generally lower than reported in clinical trials, probably due to the short revision period. Treatment was generally well tolerated in most patients, and adverse events were easily controlled, preventing patients from discontinuing treatment permanently. Further research will be needed to determine whether delays/temporary interruptions of treatment and dose reductions might affect its efficacy in the long term.

References and/or acknowledgements No conflict of interest.