Second Primary Lung Cancer Risk Assessment Tool (SPLC-RAT) is a web-based risk prediction tool for second primary lung cancer (SPLC) among patients with initial primary lung cancer (IPLC) who ever smoked before lung cancer diagnosis. By simply entering patients’ demographic data, tumor characteristics, and smoking history, the estimates for 5-year and 10-year risks of developing SPLC after initial diagnosis of lung cancer can be provided.