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Year 2000 Standard Report

CBTRUS incidence rates adjusted using the Year 2000 United States standard population.

The objective of this report is to provide new estimates on the incidence of all primary brain tumors, both malignant and benign, using the recently recommended Year 2000 United States standard population. CBTRUS data were available for the five-year period 1990-1994, from 11 collaborating state cancer registries. Incidence rates adjusted using the 1970 United States standard population were previously reported in the CBTRUS 1997 Annual Report. These new estimates are a better reflection of incidence in the current population. Estimates to the Year 2000 United States standard population should not be compared to estimates adjusted to other populations.

BACKGROUND

The use of standard populations to calculate adjusted rates is a fundamental epidemiologic tool that allows the comparison of rates among populations by controlling for the variation in age, gender and race distributions among the groups. Cancer incidence rates in the United States have traditionally been standardized to the 1970 U.S. population. The Year 2000 standard reflects the aging of the population and was recently chosen for a new standard as it more closely represents the current age distribution of the population1. This change has broad implications for the descriptive epidemiology of all health events as estimates of disease incidence will change. Implementation of the Year 2000 standard by existing surveillance systems in the United States is currently in progress. To explore the reporting and policy implications associated with using this new standard, the Central Brain Tumor Registry of the United States (CBTRUS) calculated age-adjusted incidence rates of intracranial tumors using the new Year 2000 U.S. standard, and contrasted them to previously published rates adjusted using the 1970 U.S. standard population.

METHODS

CBTRUS obtained non-confidential incidence data from 12 collaborating state cancer registries that collect incidence data on all primary brain and central nervous system tumors (Table 1). The Virginia registry provided 1994 data only, the first year for which benign brain tumor data were available in that state. As in the CBTRUS 1997 Annual Report, Virginia data were not included in the Year 2000 standard incidence calculations. Data were requested for all cases diagnosed from 1990-1994 with a primary tumor at any of the following sites: brain (International Classification of Diseases for Oncology2 topography codes C71.0-C71.9), meninges (C70.0-C70.9), spinal cord, cranial nerves, and other parts of the central nervous system (C72.0-C72.9), and pituitary and pineal glands (C75.1-C75.3). Yearly population data by five-year age groups for each state were obtained from the SEER web site3.

To edit the state data, CBTRUS used a modified metafile from a computer editing program4 that generates warnings when illogical or impossible site, behavior, and/or morphology codes are detected. Queries about possible errors were sent to each collaborating registry for review and correction as needed. CBTRUS was unable to use CBTRUS computer data editing for two registries, Connecticut and Massachusetts, as they submitted data in an incompatible format. Corrected data were incorporated into the CBTRUS data base and aggregate descriptive statistics calculated.

Age-adjusted incidence rates for all primary brain tumors by gender, race and tumor type using the 1970 U.S. standard population have been previously published5. Using Year 2000 population projections available from the Bureau of Census6, CBTRUS adjusted CBTRUS incidence data using the Year 2000 standard population in five-year age categories. Age-adjusted incidence rates per 100,000 person-years and 95 percent confidence intervals were estimated using SAS7. The percent change in rates adjusted with the Year 2000 standard from rates adjusted to the 1970 standard was computed to illustrate the impact of using the new standard population.

Classification by histology

CBTRUS histology groupings were developed in collaboration with the CBTRUS consulting pathologist, Dr. Janet Bruner, of the University of Texas M.D. Anderson Cancer Center. These groupings which aim for improved clinical relevance utilize ICDO-morphology codes and are broadly based on the new World Health Organization (WHO) categories for brain tumors8. The listing of ICDO-morphology codes included in each grouping is presented in Table 1.

See Table 2 for a list of the participating registries in CBTRUS.

RESULTS

The incidence rates for the major histology groupings using the Year 2000 standard are shown in Table 2000-1. When compared to previous data adjusted using the 1970 standard shown in Table 3, the overall incidence of brain and CNS tumors adjusted with the new standard rose from 11.5 per 100,000 person-years to 12.8 per 100,000 person-years (Table 2000-1). This 11.8 percent increase is strictly an artifact of the change in standard used and does not reflect a true increase in rates. Similarly overall rates in males and females increased from 12.1 to 13.6 and from 11.0 to 12.3 respectively. Rates increased for most of the major histology groupings as the Year 2000 standard reflects the aging of the population and these tumors are more common in older age groups. The exception was that rates for germ cell tumors and cysts that occur more often at a younger age decreased slightly after using the new standard population.

The proportion of brain tumors by histology is shown in Table 2000-2. This table shows the incidence rate by histology. The incidence rates have also been adjusted using the 1970 standard population so that one can observe the artifactual change in incidence rates which is due to using a more current standard. The largest increase in incidence rate was observed for meningiomas that rose from 2.63 to 3.15 (19.8%). These tumors are the most frequently reported histology and have an older average age at diagnosis. The rate for glioblastomas, the second most frequently reported tumor, increased from 2.60 to 2.94. Rates for two predominately pediatric tumors, pilocytic astrocytomas and embryonal tumors (including medulloblastomas), decreased from 0.27 to 0.22 (18.5%) and 0.26 to 0.22 (15.4%) respectively after adjusting with the new standard. Rates for some histologies, including anaplastic oligodendrogliomas and malignant gliomas were virtually unchanged. Rates for anaplastic astrocytomas, oligodendrogliomas, and ependymomas increased slightly.

The histology-specific rates by gender are presented in Table 2000-3. Overall rates are higher in males (13.55) than females (12.25). Tumors with a higher incidence in males relative to females include germ cell tumors, lymphomas, medulloblastomas, oligodendrogliomas, glioblastomas, and astrocytomas. Meningioma rates are higher in females than males. The histology-specific rates by race are presented in Table 2000-4. Overall rates are 1.5 times higher in whites as compared to blacks. Incidence rates are higher in whites for several histologies including diffuse astrocytomas, anaplastic astrocytomas, glioblastomas, oligodendrogliomas, ependymomas, mixed gliomas, unspecified astrocytomas, nerve sheath tumors, hemangioblastomas, and germ cell tumors. The pattern of rates by gender and race is similar to what was previously reported using the 1970 standard. The male to female ratio for all primary brain tumors is 1.1 after adjustment using the 1970 and 2000 standard populations. The change in incidence rate is a reflection of the standard population used and is not a change in disease occurrence.

The age-specific incidence rates for the most common histologies are presented in Table 5. By definition, age-specific rates are not adjusted. Therefore, these rates are identical to the information presented in the 1997 CBTRUS Annual Report. Brain tumor incidence for all primary tumors increases with increasing age at diagnosis and peaks in the 75-84 year old age group.

Incidence rates for the childhood tumors (age at diagnosis less than 20 years) by gender adjusted using the Year 2000 standard are shown in Table 2000-5. Rates are higher in males than females. The most common histologies in this age group are medulloblastomas, pilocytic astrocytomas, and unspecified astrocytomas. The total incidence rates for all tumors in children were virtually identical when estimated with the two standards. The age-specific rates for the pediatric tumors are shown in Table 2000-6.

SUMMARY

As the overall incidence of brain and CNS tumors rises with increasing age, and the Year 2000 standard population reflects the aging of the U.S. population, it is expected that the summary adjusted rate using the Year 2000 standard is higher than those previously reported using the 1970 standard. The increase in rates was not uniformly observed for the various histologies located within the CNS, because of their different age, race, and sex distributions. It is valid to compare population-based disease rates only when they have been adjusted to the same standard population. It will be important to carefully report and document the artifactual changes in incidence rates associated with using the new Year 2000 population standard so that it does not add unnecessarily to the controversy surrounding the increasing incidence in brain tumors. These new estimates provide a baseline against which further reports using the currently recommended Year 2000 standard can be compared.

REFERENCES

1. Anderson RN, Rosenberg HM. Age standardization of death rates: implementation of the Year 2000 Standard. National vital statistics report; vol. 47 no3. Hyattsville, Maryland: National Center for Health Statistics, 1998.
2. Percy C, Van Holten V, Muir CM (Eds). International Classification of Diseases for Oncology. 2nd edition. Geneva, Switzerland, 1990.
3. Reis LAG, Kosary CL, Hankey BF, Miller BA, Edwards BK (Eds) SEER Cancer Statistics Review 1973-1995. SEER Web Site. Cited November 11, 1997. World Wide Web URL: http://www-seer.ims.nci.nih.gov/
4. EDITS version 2.00 (Feb. 7, 1997) Division of Cancer Prevention and Control, National Center for Chronic Disease Prevention and Health Promotion. Centers for Disease Control, U.S. Public Health Service, Department of Health and Human Services..
5. Surawicz TS, McCarthy BJ, Kupelian V, Jukich PJ, Bruner JM, Davis FG, and the collaborating registries of the CBTRUS. Descriptive epidemiology of primary brain and CNS tumors: Results from the Central Brain Tumor Registry of the United States, 1990-1994. Neuro-Oncology [serial online], Doc. 98-13, January 19, 1999. World Wide Web URL: http://neuro-oncology.mc.duke.edu
6. U.S. Bureau of the Census. Population projections of the United States by age, sex, race and Hispanic origin: 1995 to 2050 (middle series). Released March 1996. Cited October 13, 1998. World Wide Web URL: http://www.census.gov
7. SASR version 6, Cary, NC: SAS Institute, 1988
8. Kleihues P, Burger PC, and Scheithauer BW (1993) The new WHO classification of brain tumors. Brain Pathology, 3: 255-268

Disclaimer
The Central Brain Tumor Registry of the United States (CBTRUS) is a not-for-profit corporation which gathers and disseminates epidemiologic data on primary brain tumors in order to facilitate research and establish awareness of the disease. CBTRUS makes no representations or warranties, and gives no other assurances or guarantees, express or implied, with respect to the accuracy or completeness of the data presented. The information provided in this website is not intended to assist in the evaluation, diagnosis or treatment of individual diseases. Persons with questions regarding individual diseases should contact their own physician to obtain medical assistance.