We created nearly 500 potential predictors of a second breast cancer event from the automated data. The occurrence of a second breast cancer event was ascertained from medical record review and served as the gold standard. We specified a range of costs for misclassifying a true event as a non-event and vice versa in CART to develop a “menu&rdquo of algorithms that researchers can select from based on whether their priority is sensitivity, specificity, or positive predictive value when identifying second breast cancer events from automated data. The algorithms were parsimonious with good accuracy and have the potential to increase efficiency and reduce costs of epidemiologic and health services research on breast cancer treatment effectiveness and outcomes.