Return to Table of ContentsBreast cancer is the most commonly diagnosed cancer among women of any race/ethnic group in California, accounting for nearly one in every three new invasive cancers diagnosed among women each year (Figure 1.1) (1). It is second only to lung cancer as a leading cause of cancer-related deaths: one in every six cancer-related deaths among California women is due to breast cancer. Based on current incidence and mortality rates, it is projected that in 1996 approximately 19,990 women in California will be diagnosed with invasive breast cancer, and 4,345 will die of the disease (2).
Legislation creating the California Cancer Registry (CCR) was passed in 1985 in response to concerns in the community about a perceived increase in cancer. Statewide collection of information on incident cancers was implemented in 1988 under the Statewide Cancer Reporting Law (Sections 210, 211.3, and 211.5 of the Health and Safety Code). The CCR is a partnership between the California Department of Health Services, the California Public Health Foundation, and ten regional cancer registries. In 1993, the Breast Cancer Act, which created the Breast Cancer Fund, was approved by the California Legislature. The legislation increased the cigarette tax by two cents per pack to generate funds to fight breast cancer. Five percent of the revenue has been allocated to support CCR surveillance activities. Data from the CCR has enabled researchers to perform numerous scientific studies on important aspects of cancer biology, epidemiology, and prevention (3). The state cancer surveillance system utilizes CCR data to monitor cancer trends and risk over time by geographic region, age, sex, race/ethnicity, and other characteristics of the California population.
Since 1991, the CCR has published annual reports with detailed information on the risk of developing and dying from cancer in California. The present report is devoted solely to breast cancer, and is part of continuing efforts by the CCR to prevent and control this disease in California. This special report covers relevant information on breast cancer which is currently collected by the CCR. Descriptive data on female breast cancer incidence, mortality, detailed site and histology, stage at diagnosis, and surgical treatment are presented. Estimates of the risk or probability of developing breast cancer are given for the four largest race/ethnic groups in California. Current data from the Behavioral Risk Factor Surveillance System (BRFSS) on screening for breast cancer are also included. Male breast cancer, a rare disease that shares some of the features of female breast cancer, is also addressed. An evaluation of breast cancer survival in California is a high priority for the CCR, but requires more complete follow-up information than is currently available.
The biology of breast cancer is extremely complex and still poorly understood. Epidemiologic studies have helped to uncover several genetic, hormonal, and environmental risk factors for breast cancer, although none of these can reliably predict which women will develop breast cancer. Among known risk factors, a family history of breast cancer (mother and/or sister), being born in the United States or Northern Europe, a previous history of cancer in one breast, and certain hyperplastic lesions have been shown to be highly correlated with breast cancer (4). Women with these characteristics are at least twice as likely to develop breast cancer as their counterparts. Moderate to high doses of radiation to the chest have also been shown to increase the risk for breast cancer, particularly among women exposed before 40 years of age (4). The long-term effects of low doses of radiation, such as those from occupational exposures or medical diagnostic procedures, have not yet been established. Some reproductive risk factors are nulliparity, late age at first full term pregnancy, and early onset of menarche (4). The relationship between breast cancer and reproductive history suggests a crucial role of ovarian hormones in the development of breast tumors. Obesity in postmenopausal women has also been associated with a higher risk for breast cancer, whereas in premenopausal women, obesity seems to be associated with a lower risk (4). Protective effects of regular physical exercise (5) and a healthy diet have also been postulated, although the link between diet and breast cancer has not yet been firmly established (6,7). Differences in breast cancer risk detected by demographic factors have been useful in formulating etiologic hypotheses and suggesting new research leads. For example, increasing age, high socioeconomic status, and urban residence are demographic factors shown to be associated with a higher risk for breast cancer (4).
From a public health standpoint, the identification of groups at higher risk for breast cancer is essential for directing preventive efforts to these groups. Race/ethnic and regional disparities in breast cancer incidence and mortality reinforce the continued need for both surveillance and the dissemination of relevant information on breast cancer in California.
Invasive female breast cancer incidence in the Bay Area, where a population-based registry has existed since 1973, climbed from 94 per 100,000 in 1980 to 123 in 1987 (8). Since 1987, incidence rates have decreased and appear to have leveled off. Because of the widespread use in recent years of mammography for breast cancer screening, more tumors have been diagnosed at earlier stages. It is possible that the apparent increase in incidence rates registered during the early 80's was due primarily to early detection screening efforts. However, the extent to which screening patterns are responsible for fluctuations in breast cancer incidence rates remains uncertain. In California, age adjusted incidence rates dropped from 111.8 per 100,000 in 1988 to 106.0 per 100,000 in 1991, and have dropped to 102.0 in 1993 (1). These rates, however, varied markedly by race/ethnicity during the same time-period. Incidence rates have been consistently higher among white non-Hispanic women (113.7 per 100,000 in 1993). Black women had the second highest rate in 1993 (94.8 per 100,000), while Hispanic and Asian/Other women had the lowest rates (66.1 and 60.0 per 100,000, respectively).
Mortality rates due to breast cancer have remained relatively constant in the United States during the last three decades. In California, a decrease in breast cancer mortality has been registered since 1985, but it has been consistent and statistically significant for non-Hispanic white women only.
The lifetime risk of developing breast cancer is a statistic frequently cited in the press. However, there is a concern that lifetime risk has been misinterpreted by many as a short term probability, rather than a long term projection. Estimates of risk over shorter time periods may be more accurate and easier to understand. For example, one in eight newborn females is expected to eventually be diagnosed with invasive breast cancer. On the other hand, among California women who are now 50 years old and cancer-free, one in 42 is expected to be diagnosed with breast cancer within ten years, and one in 18 within 20 years.
Routine breast cancer screening can diagnose cancers at an earlier stage, when the likelihood of survival is higher. The value of screening mammography in women over 50 years of age is undisputed. For women between 40 to 49 years of age, the potential benefits of routine mammography are still controversial. The percent of California women age 50 and older who reported having had a screening mammogram within the last year increased from 29% in 1987 to 58% in 1994. Overall, California has already achieved the Federal government's Healthy People 2000 goal of at least 60% of women 50 years and older receiving a screening mammogram in the two previous years (9). Although mammography utilization has increased substantially in California, women reporting low income and low educational attainment are still screened less often.
Early diagnosis increases the likelihood of surviving breast cancer. Follow-up on breast cancer cases reported to the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) Program from 1986 to 1991 show that, among women diagnosed while the tumor was still confined to the breast tissue, 96% were alive after five years (10). In contrast, only 20% of women diagnosed after the cancer had metastasized to distant parts of the body survived the first five years (10). From 1988 to 1992, there was a trend for earlier diagnosis among California women with breast cancer, particularly for those over 50 years of age. Despite this encouraging trend, regional, socioeconomic, and race/ethnic differences in stage at diagnosis were detected during the period. Black and Hispanic women were less likely to be diagnosed at earlier stages than non-Hispanic white or Asian women. Differences were more manifest in the lower socioeconomic groups. From a public health perspective, these findings reinforce the need to expand access to low-cost early breast cancer detection services for women in low-income, ethnic minority, and low educational attainment groups.
Breast-conserving surgery (BCS) is now considered a safe alternative to mastectomy for most women with early stage breast cancer. In recent years, California has witnessed a marked increase in the use of breast-conserving techniques. Although the proportion of women receiving this type of surgery differs by demographic characteristics, trends for increased utilization of BCS were statistically significant in all reporting regions, and for all age, race/ethnic, and socioeconomic groups.
The present report is only one of the steps taken by the CCR towards the promotion of a better understanding of the epidemiology of breast cancer in California. For example, the Breast Cancer Act of 1993 has made possible the "California Teachers Study", conducted jointly by the Department of Health Services, the University of Southern California, the University of California at Irvine, and the Northern California Cancer Center. This large prospective research project, currently under way, should provide invaluable information to elucidate the causes of breast cancer.
Breast cancer still threatens the lives and quality of life of thousands of California women. However, many positive changes in breast cancer management have occurred in recent years, particularly for women with an early-stage diagnosis. Improvements in medical technology, a better understanding of how breast cancer develops and spreads, and the assertiveness of those concerned with women's health were responsible for these changes. The CCR has made significant contributions to the body of knowledge on breast cancer, and is committed to continued support of efforts to prevent and control this deadly disease in California.
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