CORRESPONDENCE

Influence of Rules From the Tenth Revision of the International Classification of Diseases on U.S. Cancer Mortality Trends

Ahmedin Jemal, Elizabeth Ward, Robert N. Anderson, Michael J. Thun

Affiliations of authors: Epidemiology and Surveillance Research, American Cancer Society, Atlanta, GA (AJ, EW, MJT); Division of Vital Statistics, National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, MD (RNA).

Correspondence to: Ahmedin Jemal, DVM, PhD, Epidemiology and Surveillance Research, American Cancer Society, 1599 Clifton Rd., Atlanta, GA 30329 (e-mail: ajemal{at}cancer.org)

One important measure of progress against cancer is the temporal trend in mortality from all cancers combined (1). Death rates from all cancers combined increased in the United States from the 1930s, when national record keeping was instituted, until 1991 and then decreased (2,3). However, the most recent annual report to the nation on the status of cancer reported that the death rate from all cancers combined was essentially constant between 1998 and 2000 (4). The report noted that the stabilization is due in part to changes in coding rules for underlying cause of death in the Tenth Revision of the International Classification of Diseases (ICD-10), which increased the number of deaths for which cancer was classified as the underlying cause by approximately 0.7%. In this correspondence, we further elaborate on the contribution of the implementation of the ICD-10 in 1999 to the discontinuity in cancer mortality trends.

Discontinuities in mortality trends resulting from revision of the ICD can be measured by use of comparability ratios. The comparability ratio for cancer in ICD-10 compared with that in ICD-9 is 1.0068, meaning that an additional 68 per 10000 deaths are attributed to cancer as the underlying cause compared with the classification under ICD-9. This ratio was derived from a large sample of dual-coded (i.e., classified by both ICD-9 and ICD-10) death records from 1996 (5). To examine trends in cancer mortality without the influence of the change in ICD coding rules, we modified age-adjusted cancer death rates for 1999 and 2000 by multiplying the age-adjusted cancer death rates for 1999 and 2000 by the inverse of the comparability ratio (0.9932). We then analyzed the long-term trend in cancer death rates from 1975 through 2000 with a join-point model (6) with and without ICD comparability-adjusted rates for 1999 and 2000.

Without comparability adjustment, the yearly percentage change in cancer death rates was -0.1% from 1998 to 1999 and -0.6% from 1999 to 2000. After adjustment, the corresponding yearly percentage change was -0.7% and -0.6%, respectively. Although these comparability-adjusted declines (the change in rate in every year from the year before) were smaller than those reported for the preceding 3 years (Fig. 1), the join-point model for the comparability-adjusted rates showed an average annual statistically significant decrease of 1.2% in death rate from all cancers combined from 1994 through 2000. This contrasts with the model for the unadjusted rates, which showed a 1.4% decline from 1994 through 1998 and a statistically nonsignificant decreasing trend (0.3% per year) from 1998 through 2000.



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Fig. 1. Trends in cancer death rates from 1975 through 2000, with and without International Classification of Diseases (ICD) comparability adjusted rates for 1999 and 2000. Rates represented by solid lines and solid circles (1975–1998) are based on ICD-9 rules, by solid lines and open circles (1999 and 2000) are based on ICD-10 rules, and by dashed lines and solid circles (1999 and 2000) are based on the ICD comparability ratio for ICD-9.

 
The effect of changes in ICD coding on mortality trends is greatest during the first 1–2 years after the introduction of such changes but diminishes thereafter. Preliminary vital statistics data for 2001 (based on 92% of all deaths in the United States) document a 1.9% reduction in cancer death rates compared with the rate in 2000 (7). When the preliminary data for 2001 are included in the join-point analysis from 1975 through 2001, cancer death rates declined by 1.0% per year from 1991 through 2001.

We conclude that, when the change in ICD coding rules is accounted for, cancer mortality trends continued to decline, albeit at a slower rate in the most recent years. Furthermore, mortality trends continued to decline when we considered the preliminary data for 2001.

REFERENCES

1 Measurement of progress against cancer. Extramural Committee to Assess Measures of Progress Against Cancer. J Natl Cancer Inst 1990;82: 825–35.[Abstract]

2 Cole P, Rodu B. Declining cancer mortality in the United States. Cancer 1996;78: 2045–8.[CrossRef][ISI][Medline]

3 Edwards BK, Howe HL, Ries LA, Thun MJ, Rosenberg HM, Yancik R, et al. Annual report to the nation on the status of cancer, 1973–1999, featuring implications of age and aging on U.S. cancer burden. Cancer 2002;94: 2766–92.[CrossRef][ISI][Medline]

4 Weir HK, Thun MJ, Hankey BF, Ries LA, Howe HL, Wingo PA, et al. Annual report to the nation on the status of cancer, 1975–2000, featuring the uses of surveillance data for cancer prevention and control. J Natl Cancer Inst 2003;95: 1276–99.[Abstract/Free Full Text]

5 Anderson RN, Minino AM, Hoyert DL, Rosenberg HM. Comparability of cause of death between ICD-9 and ICD-10: preliminary estimates. Natl Vital Stat Rep 2001;49: 1–32.[Medline]

6 Kim HJ, Fay MP, Feuer EJ, Midthune DN. Permutation tests for joinpoint regression with applications to cancer rates [published erratum appears in Stat Med 2001;20:655]. Stat Med 2000;19: 335–51.[CrossRef][ISI][Medline]

7 Arias E, Smith BL. Deaths: preliminary data for 2001. Natl Vital Stat Rep 2003;51: 1–44.


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