Breast Cancer in New Jersey - 1979-1995
Technical Notes

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THE NEW JERSEY STATE CANCER REGISTRY

The objectives of the New Jersey State Cancer Registry (NJSCR) are to:

The New Jersey State Cancer Registry is a population-based incidence registry that serves the entire state of New Jersey, with a population of approximately 8 million people. The NJSCR was established by legislation (NJSA 26:2-104 et. seq.) and includes all cases of cancer diagnosed in New Jersey residents since October 1, 1978. New Jersey regulations (NJAC 8:57A) require the reporting of all newly diagnosed cancer cases to the NJSCR within three months of hospital discharge or six months of diagnosis, whichever is sooner. Reports are filed by hospitals, diagnosing physicians, dentists, and independent clinical laboratories. Every hospital in New Jersey is now reporting cancer cases electronically. In addition, reporting agreements are maintained with New York, Pennsylvania, Delaware, Florida, and other states so that New Jersey residents diagnosed with cancer outside the state can be identified.

All primary invasive and in situ neoplasms, except certain carcinomas of the skin, are reportable to the NJSCR. The information collected by the NJSCR includes basic patient identification, demographic characteristics of the patient, medical information on each cancer diagnosis (such as the anatomic site, histologic type and summary stage of disease), and vital status (alive or deceased) determined annually. For deceased cases, the underlying cause of death is also included. The primary site, behavior, grade, and histology of each cancer are coded according to the International Classification of Disease for Oncology, 2nd edition.15 The NJSCR follows the data standards promulgated by the North American Association of Central Cancer Registries (NAACCR), including the use of the Surveillance Epidemiology and End Results (SEER) multiple primary rules.16-20

The NJSCR is a member of NAACCR, an organization which sets standards for cancer registries, facilitates data exchange, and publishes cancer data. The NJSCR also has been a participant of the National Program of Cancer Registries sponsored by the Centers for Disease Control and Prevention since it began in 1994. In 1998, the NJSCR attained the NAACCR Gold Medal for high quality data.

The New Jersey Department of Health and Senior Services has participated in several studies of breast cancer among women and men. One study, of women under age 45 with breast cancer in Atlanta, Georgia, Seattle/Puget Sound, Washington, and five counties in central New Jersey, analyzed a series of potential risk factors for breast cancer including alcohol consumption, body size, oral contraceptives, and breast feeding.21-27 Another study involved the relationship between health insurance coverage and clinical outcomes among women with breast cancer.28 A study of men with breast cancer, using cases from ten population-based cancer registries including the NJSCR, looked at hormonal related factors such as undescended testis, removal of one or both testes, injury to testis, infections of the testis, late puberty, infertility, high blood cholesterol, rapid weight gain, benign breast conditions, and obesity.29-30 Currently, staff of the Office of Cancer Epidemiology are collaborating with the scientists who are leading a study of breast cancer among women on Long Island and are on the review committee for another study of breast cancer among women living on Cape Cod.

DATA SOURCES

The breast cancer data contained in this report are from four sources:

For this report, incident breast cancer cases diagnosed only in the invasive stages are included; the in situ stage cases are excluded, except for the section on the stage at diagnosis which includes the in situ cases (Tables 2, 11-14, Figures 7- 9). The reason for excluding the in situ cases for most of the report is that data on breast cancer incidence for the U.S. and other cancer registries published by the federal government or NAACCR do not include in situ cases or include in situ cases separately from the invasive cases. Following the SEER multiple primary rules, women could be counted more than once if they were diagnosed with two or more primary breast cancers.

The most recent data from NAACCR were used to compare New Jersey breast cancer incidence and mortality with the United States.7,8 The incidence data for the United States are based on nineteen population-based cancer registries that met criteria set by NAACCR: five years of incidence data (1989-1993); NAACCR estimates of at least 90 percent completeness; 0.1 percent duplicates or fewer, and completion and error correction of records using EDITS. The nineteen cancer registries cover 34 percent of the total U.S. population, including 34 percent of white U.S. residents and 27 percent of black U.S. residents. (See Appendix IV. for a list of the 19 cancer registries.) The nationwide mortality data for 1989 to 1993 were obtained by NAACCR from the federal Centers for Disease Control and Prevention, National Center for Health Statistics. The population estimates were from the SEER program, as were our population estimates.

DATA QUALITY

In April 1998, NAACCR awarded the NJSCR the gold standard, the highest standard possible, for the quality of the 1995 data. The criteria used to judge the quality of the data were completeness of cancer case ascertainment, completeness of certain information on the cancer cases, percent of death certificate only cases, percent of duplicate cases, passing an editing program, and timeliness. These same quality indicators applied to earlier NJSCR data also have demonstrated a high degree of accuracy and reliability of the data presented in this report.

While our estimates of completeness are very high, some cases of breast cancer among New Jersey women who were diagnosed and/or treated in other states, may not yet have been reported to us by other state registries. This fact should be considered in interpreting the data for the more recent years. However, these relatively few cases will not significantly affect the cancer rates in these years, or alter the overall trends presented in this report.

CALCULATION OF RATES

Annual population estimates for New Jersey, used to calculate incidence and mortality rates, for the years 1979 through 1994 are from the National Cancer Institute's Surveillance Epidemiology and End Results (SEER) program. Since the population estimates for 1995 were not yet ready, the estimates for 1994 were used for 1995. All the incidence and mortality rates, except age-specific rates, were age-adjusted using the 1970 U.S. Standard Population. This allows comparisons among the rates by year, race, and geographic area. An explanation of why and how the incidence and mortality rates were age-adjusted follows:

Cancer occurs at different rates in different age groups, making age a very important risk factor for cancer. Therefore, incidence and mortality rates are frequently calculated separately for specific age groups. These rates are referred to as age-specific rates. The age-specific rate for a time period of length t is calculated as follows:

Formula

where

ra = the age-specific rate for age-group a,
na = the number of events (cancer diagnoses or deaths, for example) in age-group a during the time period,
t = the length of time in years, and
Pa = average size of the population in age-group a during time t (mid-year population or average of the mid-year populations).

Multiplying ra by 100,000 expresses the rate as the number of cases per 100,000 persons.

When comparing rates across different population subgroups, e.g. by race, or across different years, it is important to account for differences in age distributions. We calculate an age-adjusted rate using a weighted-average of the age- specific rates. This method of age adjustment is known as direct age-standardization. The age-adjusted rate is obtained by using the age distribution of a standard population as the weights31:

Formula

where

R = the age-adjusted rate,
ra = the age-specific rate for age-group a, and
Std.Pa = the number of people in age group a of the standard population.

Multiplying the age-adjusted rate by 100,000 expresses it as the number of cases per 100,000 persons.

The standard population used for age adjustment throughout this report is the 1970 U.S. Standard Population. This is the traditional standard population used in much of the published cancer incidence data.


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