CBTRUS incidence rates adjusted using the Year 2000 United States standard population.
The objective of this report is to provide a current overview of the descriptive epidemiology of all primary brain tumors in the United States. CBTRUS compiles the nation's largest population-based database on primary brain and central nervous system tumors. Incidence rates of primary malignant and non-malignant brain tumors from 1992-1997 were calculated by gender, age, and race. Data on the incidence and mortality rates for malignant brain tumors are presented from the Surveillance, Epidemiology and End Results (SEER) program of the National Cancer Institute and North American Association of Central Cancer Registries (NAACCR). SEER data were also used to estimate survival rates for primary malignant central nervous system tumors.
BACKGROUND
The CBTRUS database contains the largest aggregation in the United States of population-based data on the incidence of all primary brain and central nervous system tumors. This database has been developed by compiling data from state cancer registries that include information on both benign and malignant primary brain tumors. This current report includes data from 14 state cancer registries. State cancer registries in Texas and Rhode Island have agreed to contribute their brain tumor data to future reports.
CBTRUS was incorporated in 1992 following a two-year study conducted by the American Brain Tumor Association to determine the feasibility of a central registry for all brain tumor cases. Until that time, standard data collection in the United States had been limited to malignant cases only. Benign brain tumors, however, may, and often do, impose the same costs to society in terms of medical care, case fatality and lost productivity as malignant tumors. A histologically benign tumor may produce devastating effects in a relatively short time based on its location, while a malignant tumor may not produce visible symptoms for months. In addition, as molecular markers have been discovered, it has become clear that certain benign brain tumors may become malignant over time. Therefore, in order to present a complete picture of this disease, CBTRUS believes benign brain tumor data must be collected along with malignant data.
This statistical report continues the past efforts CBTRUS has made to provide accurate, population-based incidence rates for all primary brain tumors by histology, age, gender, and race. As in previous CBTRUS reports, these data have been listed in histologic groupings with improved clinical relevance. They are useful for surveillance and may serve as a baseline for comparison with regional rates. They are also important for the allocation and planning of specialty health care services, for planning programs for disease prevention and control, and in the development of research proposals including those that investigate etiology.
CBTRUS encourages all surveillance registries to expand their primary brain tumor data collection to include tumors of benign and uncertain behavior and believes that only by having complete data will thee necessary clues be found to investigate its causes.
DEFINITION OF RATES
Rates measure the occurrence of disease in a population. They are calculated by counting the observed numbers of cases of an event occurring in a defined population within a specified time period and dividing by the total population at risk within the same time period. As an example, in this report the incidence of brain tumors in a state is calculated by adding up all the newly diagnosed cases of brain tumors within that state for the years of interest and dividing by the sum of the state population totals for the same years. Rates are expressed in units of person-time with each person-year reflecting one individual over one year. For cancer, rates are usually expressed per 100,000 person-years.
Incidence, mortality and survival rates are presented in this report. Incidence rates measure the occurrence of newly diagnosed cases of disease. Mortality rates quantify the number of people who have died from the disease. Survival rates (percents) are the probability of surviving for a specified time period. Observed survival estimates are computed from life-table estimates and yield the probability of surviving a specified time period (often five years) following diagnosis. Relative survival rates are defined as the observed probability of survival adjusted for the expected survival rate of the United States population for that age, gender, and calendar year.
The rate of disease in an entire population is the crude rate. Rates for a subset of a population are specific rates. Age-specific rates that describe the rate of disease in a defined age group are presented in this report. The variability around the estimates of incidence rates is reflected in the standard error. Rates are frequently adjusted by age, gender, and/or race. Adjusting rates to a common standard population allows for comparisons of rates across regions, by gender or race or over time. Cancer incidence rates in the United States have traditionally been adjusted to the 1970 United States standard population. The Year 2000 standard population has been recently made available, and it is a better representation of the current age distribution in the United States population.
METHODS
Data Collection
CBTRUS obtained incidence data from fourteen collaborating state cancer registries that include cases of non-malignant (benign) and malignant primary brain tumors. Data were requested from each registry on all cases newly diagnosed between 1992 and 1997 with a primary brain tumor at any of the following sites (International Classification of Diseases for Oncology (ICDO) codes in parentheses): brain (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)1. Data were received without personal identifiers. Population data for each state were obtained from the SEER program web site, which receives yearly population estimates from the U.S. Bureau of the Census2.
Eleven states provided incidence data for the entire six-year period (Figure 1). Virginia and New Mexico began collecting data on non-malignant tumors in 1994 and 1996 respectively. Maine provided data on malignant tumors only for 1992-1996.
Data were edited using a modified metafile from the EDITS3 program that generates warnings when illogical or impossible site, morphology, and/or behavior combinations are reported. Connecticut data were submitted in a different format that could not be edited electronically. When possible, queries were directed to the state cancer registry staff for correction or clarification.
Classification by histology
The histology groupings used in this report were developed in collaboration with our consulting pathologist, Dr. Janet Bruner, of the University of Texas M.D. Anderson Cancer Center. These groupings are broadly based on the World Health Organization (WHO) categories for brain tumors4. The list of ICDO-morphology codes included in each group is presented in Table 1. The classification scheme has been updated to include morphology codes that were not previously reported to CBTRUS.
Estimation of Incidence and Mortality Rates
Incidence rates were generated using SAS, a computer based statistical analysis system5. Overall rates for benign and malignant tumors and rates for selected histology groupings by gender, race, and age were estimated using data from the eleven regions that provided six years of data. Age-adjusted rates of CBTRUS data based on five-year age groupings were standardized to the 1970 and Year 2000 U.S. standard populations.
State incidence and mortality rates for malignant tumors from 1993-1997 were obtained from the most current Cancer Incidence in North America (CINA) Publication on the NAACCR web site6. These rates were adjusted using the 1970 United States standard population only. Rates adjusted to the Year 2000 standard cannot be compared to rates adjusted to the 1970 standard. Many of the CBTRUS incidence rates reported here are higher when adjusted to the U.S. 2000 standard population. The differences in incidence rates adjusted to 1970 and Year 2000 are merely an artifact of the aging of the population over this time period and should not be misinterpreted as an increase in brain tumor incidence.
Differences in Brain Tumor Definition
CBTRUS, SEER, and NAACCR categorize brain tumors differently using ICDO site, morphology, and behavior codes. The CBTRUS definition includes tumors from the brain (C71.0-9), meninges (C70.0-9), spinal cord, cranial nerves, and other parts of the central nervous system (C72.0-9), and the pituitary and pineal gland (C75.1-C75.3). CBTRUS includes all tumor morphologies located within these sites and includes all primary tumors, with a behavior code of 0 (benign), 1 (uncertain) and 3 (malignant). SEER and NAACCR's definition of brain tumors (used in their published incidence and mortality statistics) includes tumors located in the brain, meninges, and other central nervous system tumors (C70.0-9, C71.0-9, and -C72.0-9) and only includes tumors of malignant behavior (3)7. In addition SEER and NAACCR exclude lymphoma and leukemia morphologies (9590-9989) from all brain and CNS sites and malignant meningiomas (9530-9539) reported within the brain. It is important to understand these differences in definition as they prohibit the direct comparison of published rates.
Estimation of Survival Rates
The SEER*Stat 2.0 program was used to estimate two-, five- and ten-year observed and relative survival rates for primary malignant brain tumor cases diagnosed between 1973-19968. This program utilizes life-table (actuarial) methods to compute survival estimates and accounts for current follow-up. The SEER grouping for brain and other nervous system cancer included ICDO-site codes C70.0-C72.9. Lymphomas and meningiomas (morphology codes 953_ and 9590-9989) were excluded. Survival estimates for pituitary and pineal tumors were determined using the C75.1-C75.2 and C75.3 site codes. Second or later primary tumors, cases diagnosed at autopsy, cases in which race is other or unknown, and cases known to be alive but for whom follow-up time could not be calculated were excluded from the SEER analyses.
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