Abstract 242P
Background
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.
Methods
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.
Results
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 |
| Any toxicity | 0.23 | 0.69 |
| CDK4/6i dose reduction | 0.83 | 1.0 |
| CDK4/6i discontinuation | 0.13 | 0.066 |
Conclusions
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.
Clinical trial identification
Editorial acknowledgement
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.