Abstract P5-07-08: Development and validation of the “radiotherapy for older women” risk calculator
Authors: Wang Shi-Yi , Mougalian Sarah , Killelea Brigid , Herrin Jeph , Fraenkel Liana , Gross Cary , Evans Suzanne 
Published: March 2020

BACKGROUND: For many older women with early-stage breast cancer, radiotherapy (RT) reduces local recurrence but does not improve overall survival. Risk calculators provide individualized risk estimation; however, there is a paucity of risk calculators specific to the elderly, in whom competing mortality is an important consideration. This study aimed to develop and validate a risk calculator to provide older patients with accurate, personalized risk estimates for local recurrence and mortality.

METHODS: We used two existing prediction models, the Early Breast Cancer Trialist Collaboration Group prediction model for breast cancer specific outcomes and ePrognosis for life expectancy, to construct a simulation model to predict individual patient risk. This new model was used to create the “Radiotherapy for Older Women (ROW)” risk calculator. ROW predicts 5-year and 10-year risks of local recurrence and mortality, according to age, comorbidities, functional status, tumor characteristics, and RT receipt. To validate the risk calculator, we collected clinical data from all women older than 65, with newly diagnosed stage I/II breast cancer between 2001 and 2010 at our institution. Discrimination was assessed using c-statistics. Calibration was examined graphically by plotting observed versus predicted probabilities and Hosmer-Lemeshow tests (H-L tests; a p-value &lt;0.05 indicating poor calibration).

RESULTS: Based on our simulation, the 5-year all-cause mortality estimated by ROW ranged from 2% to 79%. ROW also projected the 5-year local recurrence, from 1% to 57% for patients not undergoing RT, and from 0% to 26% for patients undergoing RT. Among the 487 patients we identified in the validation study, the predicted 5-year mortality was 20%, compared to observed 5-year mortality of 16%. The predicted 5-year local recurrence rate was 3.9%, compared to observed 5-year local recurrence rate of 3.1%. The c-statistics were 0.761 for 5-year mortality and 0.775 for 5-year local recurrence. The calibration plot for 5-year local recurrence reflected good agreement between the observed outcomes and predictions; however, the model seemed to over-estimate 5-year all cause-mortality (H-L test; p=0.01). The performance for 10-year outcomes was similar (Table). A beta-version of this risk calculator can be accessed online at https://rtbreastcancer.org.

CONCLUSIONS: Based on simulation modeling without cohort data collection, the authors developed an online individualized risk calculator. The outcome estimates projected by the tool were compatible with the observed estimates from real-world data. Such individualized risk provision could facilitate shared decision-making between provider and patient. Future research collecting prospective data to validate our estimates is needed.

MortalityLocal recurrencec-statistics95% CIc-statistics95% CI5-year0.761(0.700, 0.822)0.775(0.664, 0.887)10-year0.769(0.722, 0.817)0.721(0.594, 0.849)CI: Confidence interval

Citation Format: Shi-Yi Wang, Sarah Mougalian, Brigid Killelea, Jeph Herrin, Liana Fraenkel, Cary Gross, Suzanne Evans. Development and validation of the “radiotherapy for older women” risk calculator [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-07-08.