Response Letter Regarding Article, "Postdiagnosis aspirin use associated with decreased biliary tract cancer-specific mortality in a large nationwide cohort".

We thank Zhang et al. for their interest in our article.(1) A large-scale registry database provides an exceptional opportunity to investigate BTC, a rare cancer.(1, 2) Although large databases, can provide a robust resource to investigate rare cancers, these analyses may still suffer from a lack of detailed clinical information, such as liver function and coagulation disorders, as well as from confounding due to compliance and over-counter-use of concomitant medications.