All cancer registries use the International Classification of Diseases for Oncology, Third Edition (ICD-O-3) to code the anatomic site and morphology. Cancer incidence statistics such as crude rates and age-adjusted rates include invasive cancers only, with the exception of in situ cancer of the bladder. Some tables for stage at diagnosis for female breast cancer include in situ cases, but these are not included in any count or rates of total cancer incidence. The SEER program site recode groups were used for classifying types of cancer, and all codes and site groups can be found at http://www.seer.cancer.gov/siterecode. Cancer cases among non-residents of Wisconsin and cases of unknown sex or age were omitted from all calculations.
Cancer Incidence Coding Changes
Beginning in 2001, several definitional changes occurred in some histologies and behaviors, affecting the reporting of mainly leukemias, lymphomas, and cancer of the ovary. This change is documented in the ICD-O-3 third edition. In addition, further changes were made again for hematopoietic diseases (leukemias, lymphomas and other blood disorders) beginning with 2010 diagnoses. Some hematopoietic diseases previously categorized as nonmalignant or premalignant are now considered malignant and reportable, if diagnosed in 2010 or later. These newly reportable cases (reportable in ICD-O-3 but not previously reportable in ICD-O-2) have now been added to the total cancer case count for each year starting in 2001. The counts for total cancers in Wisconsin therefore are higher for years covered by ICD-O-3, adding approximately 300 to 500 additional cases each year, due to changes in reporting requirements.
Mortality data for Wisconsin were obtained from the National Center for Health Statistics in the Centers for Disease Control and Prevention. Underlying cause of death was coded using the International Classification of Diseases (ICD). In the United States, ICD-9 was used for all deaths up to 1998 and ICD-10 was used for all deaths that occurred in 1999 and later years. A SEER mortality recode was used to classify cancer deaths into the groupings used in WISH. Cancer deaths were defined as those coded 140.0 through 208.9 and 238.6 in IDC-9 and C00 through C97 in ICD-10. Cancer deaths among non-residents of Wisconsin and deaths of unknown sex or age were omitted from all calculations. The SEER cause of death recodes can be found at: http://seer.cancer.gov/codrecode.
Cancer Mortality Coding Changes
The change from ICD-9 to ICD-10 for 1999 deaths caused some artifactual variation in trends in causes of death due to cancer. The extent of the variation has been measured in comparability studies in which death records were double coded using both the Ninth and the Tenth Revisions. The results found approximately 0.7% more deaths are assigned to cancer when ICD-10 is used than when ICD-9 is used (Anderson, et al., 2001). Therefore the overall cancer rate is higher when ICD-10 is used. The general rule does not apply to specific cancers, whose rates may be higher or lower using ICD-10. However, the differences are small; changes in mortality rates across the ICD-9 to ICD-10 boundaries are minor, especially for major sites.
Multiple Primary Determination Rules
Starting with 2007 cases, revisions were made to existing rules for determining when multiple primary cancers are present. The new rules may have an effect on the number of subsequent primaries identified, as state cancer registries changed certain rules for counting and coding multiple primaries (see the SEER website). Preliminary data suggest that rates vary marginally for most cancers as the result of this change.
Duplicate Case Records and Case Consolidation
Central cancer registries rely on multiple reporting sources to obtain all of the diagnostic and treatment information for cancer case reports. Multiple reports for the same patient must be matched and information from all matched records is then consolidated. In addition to determining whether the multiple reports refer to the same person, central cancer registry staff must also determine whether the tumor represents a new tumor or a duplicate report for a tumor already reported. As part of routine registry operations, all cases are run through standard linking procedures that are included in the registry database software application.
In addition, all data in this WISH module were consolidated using the standard consolidation and duplicate case assessment protocols and edits from the North American Association of Central Cancer Registries (NAACCR). These protocols and edits create an increase in manual review of text fields. This review allows for corrections to important merging and consolidation coded fields such as primary site, laterality and histology codes. The standard protocol for assessing duplicate cases (from the North American Association of Central Cancer Registries, NAACCR) can be found on the NAACCR website.