Validity of breast cancer surgery treatment information in a state-based cancer registry.

Surgery is an important part of early stage breast cancer treatment that affects overall survival. Many studies of surgical treatment of breast cancer rely on data sources that condition on continuous insurance coverage or treatment at specified facilities and thus under-sample populations especially affected by cancer care inequities including the uninsured and rural populations. Statewide cancer registries contain data on first course of cancer treatment for all patients diagnosed with cancer but the accuracy of these data are uncertain.