Cyclin-Dependent Kinase 4/6 inhibitors (CDK4/6i) represent the standard I-II line for hormonal receptors positive/human epidermal growth factor receptor 2 negative metastatic breast cancer (MBC) patients. Metastases directed radiotherapy (RT) for these patients is commonly used with palliative or ablative schedules during systemic treatment. There is still a lack of robust data on the safety concerning RT during CDK4/6i treatment.
Primary outcomes of our study were impact of RT on any toxicity greater than Grade 2 (>G2), any toxicity (any grade), CDK4/6i dose reduction, CDK4/6i treatment discontinuation. Analysis by simple cross-tables with p-values from chi-square test and logistic analysis to confirm emerged associations were performed.
We analyzed a series of 133 patients. We recorded the following events: 127 any toxicity (95.5%), 91 toxicity >G2 (68.4%), 62 CDK4/6i dose reduction (46.6%), and 5 treatment discontinuation (3.8%). RT was prescribed in 59 cases (16.5% sequential, 27.9% concomitant) while 74 patients did not receive RT (55.6%). Postmenopausal patients experienced significantly higher toxicity >G2 (OR 4.08; 95%CI 1.58-10.56; p=0.005). Intent of RT (palliative vs ablative) and site of RT (bone vs visceral) did not impact on primary outcomes of the study. High conformal RT techniques IMRT/CyberKnife (as compared to 2D/3D techniques) were associated to higher toxicity >G2 (OR 8.15; 95%CI 0.97-68.38; p=0.041). Overall RT (both concomitant and sequential) did not significantly impact on any of primary outcomes of the study (p-values reported in the table). Table: 242P
|Outcome||Sequential RT (n=22) vs Concomitant RT (n=37) vs No RT (n=74)||RT (n=59) vs No RT (n=74)|
|Any toxicity >G2||0.54||0.45|
|CDK4/6i dose reduction||0.83||1.0|
RT for the treatment of I-II line MBC patients receiving a CDK4/6i did not significantly impact on treatment safety profile, CDK4/6i dose reduction and discontinuation.
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All authors have declared no conflicts of interest.