Considerations When Comparing Cancer Statistics Over Time

While the Cancer Registry collects data on in situ and invasive malignant cancers, the incidence tables in this report describe invasive malignant cancers only (with the exception of in situ cancer of the bladder). Important to note are changes made to the behavior classification of some neoplasia effective in 2001, with the introduction of the 3rd Edition of the International Classification of Diseases for Oncology (ICD-O-3). Some cancers diagnosed and considered malignant prior to 2001 (based on ICD-O-2) are coded with borderline malignancy in ICD-O-3; neoplasia with borderline potential for malignancy based on ICD-O-3 are not included in these statistics. Conversely, some conditions with borderline malignant behavior based on ICD-O-2 are classified as malignant in ICD-O-3 and are, consequently, “reportable.”

Comparisons of incidence statistics for total cancers or categories that include tumors with revised behavior must be made with caution, especially when looking at statistics over time. In this report, data presented for the most recent five years, 2007-2011, include cancers classified as malignant based on ICD-O-3, which is the current standard. However, for any time trends where incidence rates are displayed by year from 1976 to 2011, the practice followed by the National Cancer Institute is used, omitting most newly-reportable cancers as well as the tumors that are no longer classified as malignant, for consistency purposes.