Clinical Predictors for Analgesic Response to Radiotherapy in Patients with Painful Bone Metastases.

BACKGROUND: Radiotherapy (RT) reduces pain in about 60% of patients with painful bone metastases, leaving many patients without clinical benefit. This study assesses predictors for RT effectiveness in patients with painful bone metastases.

MATERIALS AND METHODS: We included adult patients receiving RT for painful bone metastases in a multicenter, multinational longitudinal observational study. Pain response within 8 weeks was defined as ≥2-point decrease on a 0-10 pain score scale, without increase in analgesics; or a decrease in analgesics of ≥25% without increase in pain score. Potential predictors were related to patient demographics, RT administration, pain characteristics, tumor characteristics, depression and inflammation (C-reactive protein [CRP]). Multivariate logistic regression analysis with multiple imputation of missing data were applied to identify predictors of RT response.

RESULTS: Of 513 eligible patients, 460 patients (90 %) were included in the regression model. 224 patients (44%, 95% confidence interval (CI) 39%-48%) responded to RT. Better Karnofsky performance status (Odds ratio (OR) 1.39, CI 1.15-1.68), breast cancer (OR 2.54, CI 1.12-5.73), prostate cancer (OR 2.83, CI 1.27-6.33) and soft tissue expansion (OR 2.00, CI 1.23-3.25) predicted RT response. Corticosteroids were a negative predictor (OR 0.57, CI 0.37-0.88). Single and multiple fraction RT had similar response. The discriminative ability of the model was moderate; C-statistic 0.69.

CONCLUSION: This study supports previous findings that better performance status and type of cancer diagnosis predicts analgesic RT response, and new data showing that soft tissue expansion predicts RT response and that corticosteroids is a negative predictor for RT response in patients with painful bone metastases.