Authors (including presenting author) :
Chou YC (1)(2), So KH (3), Lim WL (1), Zhou KR (2)
Affiliation :
(1) Department of Pharmacy, Prince of Wales Hospital, (2) School of Pharmacy, the Chinese University of Hong Kong, (3) Department of Pharmacy, Tuen Mun Hospital
Introduction :
Up to April 2024, three CDK 4/6 inhibitors were licensed in Hong Kong: palbociclib, ribociclib and abemaciclib. All three agents were licensed for the treatment of ER-positive, HER2-negative advanced or metastatic breast cancer, with individual agents having additional indications in other patient arms.
Objectives :
Following the results of the landmark trials, we hypothesized that ribociclib would have a significantly greater rate of treatment modification compared with palbociclib and abemaciclib. Moreover, exploratory risk factor analysis was performed in the hope to guide the treatment
choices and hopefully could facilitate the development of a personalized therapy of CDK 4/6 inhibitors.
Methodology :
The study was a single-center retrospective three-arm cohort study conducted at the Prince of Wales Hospital (PWH). Patients who were 18 years of age and older, diagnosed with ER-positive, HER2-negative locally advanced or metastatic breast cancer, and were started on any of the three CDK 4/6 inhibitors from January 2019 to December 2022 in PWH were recruited. Electronic patient records were reviewed to capture the rate of treatment modification (composite of treatment interruption, dose reduction and treatment discontinuation). Each of these outcomes were also individually analyzed. Logistic regressions were performed to identify possible significant risk factors for treatment modification.
Result & Outcome :
A total of 193 patients were included in the study (palbociclib n=66 patients; ribociclib n=78; abemaciclib n=49). The overall rate of treatment modification did not differ significantly between any of the treatment pairs. Treatment interruption rate was significantly lower for patients receiving abemaciclib compared to those receiving palbociclib (p=0.007) and ribociclib (p< 0.001). However, no significant differences were observed for other components. Absolute neutrophil count (ANC) ≤3.7x10^9/L (p=0.004) was identified as the only significant risk factor for treatment modification in the palbociclib group. In the ribociclib group, ANC≤3.7x10^9/L (p=0.009) was a significant risk factor, while the use of topical steroids as premedication (p=0.044) and the presence of bone metastasis (p=0.025) were identified as negative risk factors for treatment modification. No significant risk factors were identified for the abemaciclib group.
There was no significant difference between the tolerability in terms of treatment modification for palbociclib, ribociclib and abemaciclib. Palbociclib and ribociclib should be used with caution in people with low baseline ANC.
