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Recent Incidence Trends
The recent decline in annual breast cancer incidence rates after several years of increasing rates among New Jersey women follows the national pattern. Starting in the 1980s, more women used screening methods such as mammography which identify breast cancer early. This may explain at least part of the increase in the breast cancer incidence rate among New Jersey women between 1979 and 1988. The subsequent drop in the incidence rate after 1988 may be because some women who would have been diagnosed after 1988 with later stage disease already had been diagnosed.10
Recent Mortality Trends
The annual age-adjusted mortality rate of female breast cancer in New Jersey also decreased in 1992 through 1995. This decrease may be due to women using screening methods that identify breast cancer early, since the survival rate for women with breast cancer diagnosed in the early stages (in situ or localized) is much greater than the survival rate for women with breast cancer diagnosed in the later stages. In recent years the annual percent of breast cancer cases among New Jersey women diagnosed in the early stages has increased greatly, from 49 percent in 1985 to 64 percent in 1995. This data on the stage of breast cancer at diagnosis are consistent with the increase between 1991 and 1995 in the estimated percentage of New Jersey women over 40 who had ever had a mammogram.
Recent Incidence and Mortality Trends - Differences Between White and Black Women
While the overall picture of breast cancer among New Jersey women is encouraging, there is need for improvement, particularly for some groups of women. The decrease in breast cancer incidence rates and mortality rates appears not to have occurred among black women as consistently as among white women. And, although black women's annual incidence rates were lower than those of white women, black women's mortality rates were higher than white women's mortality rates in the most recent years. The reasons for black women's lower incidence of breast cancer may be due partially to differences in risk factors.11 The higher mortality rates among black women may be explained by a higher percentage of breast cancers being diagnosed in the later stages and differences in the tumors, socio-economic factors, and treatment.12 In New Jersey, between 1985 and 1995 a higher percentage of the breast cancers diagnosed in black women were diagnosed in the later stages than were the breast cancers diagnosed in white women, though the gap is closing.
The mammography screening data show an improvement between 1991 and 1995 in the percentage of women of age 40 and over who ever had a mammogram, but did not show as much of an improvement in the percentage of women of age 40 and over who had a mammogram in the previous two years.
Comparison of New Jersey and U.S. Rates
Why the breast cancer incidence rates and mortality rates among New Jersey women are higher than the U.S. rates is not completely understood, but the answer probably lies in a combination of known risk factors for breast cancer and in other risk factors which are as yet unknown. Several recent studies have found that known breast cancer risk factors explain much of the differences in breast cancer incidence rates and mortality rates among the different regions of the country.12-14
A very recent cohort study compared breast cancer incidence and mortality among women in the Northeast, California, the Midwest, and the South.12 The researchers did not find an excess in breast cancer rates in the Northeast after adjusting for age and many known breast cancer risk factors (menopausal status, age at menopause, age at first menstruation, number of live births, age at first full-term pregnancy, use of oral contraceptives, use and duration of use of postmenopausal hormone therapy, history of breast cancer in mother or sister, history of benign breast disease, height, and current and past body mass index). An earlier study found that fifty percent of the excess in breast cancer mortality among white women in the Northeast compared to the South (the region of the country with the lowest breast cancer mortality rates) was explained by several recognized breast cancer risk factors.13 Yet another study found that elevated breast cancer incidence rates in the San Francisco Bay Area, which has the highest rates in the country, were completely accounted for by regional differences in the known risk factors for breast cancer.14
Breast cancer incidence has recently declined in New Jersey and the U.S. However, the rates in New Jersey remain higher than in the U.S. While white women are more likely to get breast cancer than black women, black women are more likely to be diagnosed at a later stage and are more likely to die of the disease. Additional research is needed on the causes and the means to prevent breast cancer. Since, at this time, early detection and treatment are the best methods to prevent mortality due to breast cancer, additional efforts are needed to reach women, particularly black women and older women, with early screening methods such as mammography.