Fig. 5

HRs, SIRs, and RRs for second primary malignancy, stratified by the demographic and clinical characteristics of patients. a Comparison of risk of SPM between subgroups by estimating HRs through Fine-Gray’s competing risk analyses. b External comparison of PORT-associated risk by estimating SIRs, taking the general population as a reference. c Internal comparison of PORT-associated risk by estimating RRs. HR hazard ratio, SIR standardized incidence ratio, RR relative risk, PORT postoperative radiotherapy