PREDICT version 3.1 overestimates survival in older women with breast cancer: a population-based external validation.

BACKGROUND: Prediction models can guide breast cancer treatment decisions by estimating individualized prognosis and treatment benefit. Since older women with breast cancer are more heterogeneous and face more competing non-breast cancer mortality, model performance may differ from that observed in the general breast cancer population. We externally validated PREDICT version 3.1 in a population-based cohort of Dutch older women with breast cancer. METHODS: Women aged ≥70 years with breast cancer were included from the Dutch Cancer Registry. Observed 5- and 10-year overall survival (OS) were estimated using Kaplan-Meier methods and compared with predicted outcomes. Calibration was assessed using smooth calibration curves and observed/expected (O/E) ratios. Discrimination was evaluated with area under the curve (AUC). Performance was examined across age groups and comorbidity strata. RESULTS: We included 11.041 women (median age 75.8 years, IQR 72.8-81.6). PREDICT v3.1 overestimated 5-year OS by 7.2% (95% CI = 6.3-8.0) and 10-year OS by 12.1% (95% CI = 11.1-13.1). Calibration plots showed deviation from the ideal line and the O/E ratio was 1.39 (95% CI = 1.34-1.44) for 5-year and 1.30 (95% CI = 1.27-1.34) for 10-year. The AUC for 5- and 10-year OS was 0.75 (95% CI = 0.74-0.76) and 0.76 (95% CI = 0.75-0.77), respectively. Overestimation of survival increased with age and number of comorbidities. CONCLUSION: PREDICT v3.1 overestimates survival in older women, particularly those with comorbidities and increased age. Despite moderate discrimination, poor calibration limits clinical applicability in this population.