OBJECTIVES : The objectives of this study are to assess the real-world treatment patterns of cyclin-dependent kinase inhibitors 4/6 (CDKi) in women with advanced breast cancer (BCa) and to assess the occurrence of dose modifications.

METHODS : This retrospective study included adult women who initiate CDKi 4/6 (ribociclib or palbociclib) between 1 March 2019 and 31 December 2019 and were diagnosed with HR-positive/HER2-negative BCa. Data was obtained through the records from Portuguese Hospital pharmacies from the participating investigation centers. Descriptive statistics were presented in this preliminary analysis. The final study results will be available for poster presentation (expected sample: 355 patients).

RESULTS : A total of 44 women, from 3 Hospitals, were included in this preliminary analysis, with a mean (standard deviation: SD) age of 59 (11) years. Overall, 63.6% received palbociclib and 36.4% ribociclib. Among the patients treated with ribociclib, 62.5% were in first line-treatment and 37.5% in second-line treatment, compared with 7.1% and 92.9% of palbociclib treated patients, respectively. The most common concomitant therapies with both CDKi were aromatase inhibitors, namely letrozol. The proportion of patients with dose modification is 25% in both CDKi 4/6 treatments within the first six months after treatment initiation. The mean (SD) doses are 487 mg (169) and 122 mg (8) of ribociclib and palbociclib, respectively.

CONCLUSIONS : This study highlights the treatment patterns for BCa with the only two reimbursed CDKi when this study was planned. With the results of this study we aim to understand if real world evidence reinforces clinical trials results in terms of dose reduction and evaluate the treatment patterns and dose modifications.