Surveillance, Epidemiology and End Results (SEER) data from the Nation
al Cancer Institute (NCI) provide reliable information about cancer in
cidence. However, because SEER data are geographically limited and hav
e a 2-year time lag, we evaluated whether Medicare data could provide
timely information on cancer incidence. Comparing Medicare women hospi
talized for breast cancer with women reported to SEER, Medicare data h
ad high specificity (96.6 percent), yet low sensitivity (59.4 percent)
. We conclude that Medicare hospitalization data can identify incident
cases for cancers that usually require inpatient hospitalization. For
cancers that often only receive outpatient treatment, such as breast
cancer, additional Medicare data, such as physician bills, are needed
to understand the entirety of treatment practices.