Orange County Voices : COMMENTARY ON HEALTH : Hunt Goes On for Clues to Higher Rate of Breast Cancer Locally : The incidence here is twice that of the nation. Lifestyle, delayed pregnancies and a UCI study may hold answers.
The breast cancer incidence rate in the United States has been rising at a rate of 1% to 2% per year for more than 20 years. For most of this time, the increase has been largely confined to post-menopausal women. However, in Orange County the rate of increase over the past 10 years has been twice as high as the rest of the nation, 3% to 4% per year, and the increases are appearing in both old and young women.
To date there is no full explanation for the cause of the increases in breast cancer in Orange County. However, it is due in part to changes in women’s reproductive behavior. In addition, the increase appears to relate primarily to earlier diagnosis, suggesting that there was more intensive screening for breast cancer during the period 1985-1989 in Orange County.
A number of risk factors may have also contributed to the increase in breast cancer incidence rates. These include suggested links of breast cancer with oral contraceptive use at young ages, moderate levels of alcohol consumption and adolescent dietary patterns.
Although initial reports found no association between oral contraceptives and breast-cancer risk, more recent results found a two-fold increase in risk associated with use of oral contraceptives by younger women. However, studies that focused on younger women (under 36 years old), found a relationship of risk with years of usage of oral contraceptive.
The effect of alcohol consumption, however, is better defined. A number of investigations have now shown a direct relationship between alcohol use and risk of breast cancer. Of concern is that in these studies, even moderate levels of alcohol consumption generally appear to be associated with elevations in risk. More studies are needed to evaluate specific patterns of drinking in relation to how the body reacts to it.
A person’s physique is also a factor. Large body size has been identified as a breast-cancer risk factor in some studies. Some investigators have observed a positive association of skeletal dimensions and breast-cancer risk. Tall women with large bony structures, or women of average height but who are overweight or obese, appear more at risk. Although skeletal dimensions are highly heritable, diet and habits may influence the body size and its susceptibility to development of breast cancer. The positive relation of body weight and breast-cancer risk appears to be limited to post-menopausal women. Several studies reported that long-term athletic training, which influences body weight, was associated with lower risk of breast cancer. But, the relation of physical activity and breast-cancer risk, especially in younger women, has not been adequately explored.
There has, however, been a lot of research devoted to the association between diet, particularly total fat consumption, and breast cancer. But the results are still inconclusive. Cross-cultural differences in fat and fiber intake, estrogen levels and breast-cancer incidence have led to relating high fat (particularly animal fats) and low fiber intake with breast cancer incidence. For example, Latino women, who eat a high fiber, lower animal fat diet, are at a much lower risk for breast cancer than whites. Some of it is genetic, but a good part of it may be diet-related.
The age when pregnancy occurs and the length of time between pregnancies may also affect a woman’s risk factor. Late age at first birth has long been recognized as a risk factor for breast cancer, but recently it has been noted that this may not apply to women under age 35 who get breast cancer. However, the majority of breast cancers occur over age 35 and are associated with women who have their first child at an older age, and have few and widely spaced pregnancies. Both characteristics are common in Orange County women.
There is an urgent need for biological markers that may help to identify women who are at high risk for developing breast cancer.
Unfortunately, identification of high-risk populations is difficult because breast cancer is a highly complex and ill-defined disease. The clinical progression of primary breast cancer varies considerably from patient to patient. Family studies of breast cancer strongly suggest genetic differences, in that the risk among relatives of breast cancer patients, particularly in younger women, are considerably higher than those with no family history.
Results of a recent population study indicate that more than 6.5 per 1,000 women are carriers of an inherited breast cancer gene, which increases their lifetime risk of breast cancer to 92%. Within Orange County alone, we estimate that there are now about 7,500 female gene carriers, who, left unidentified, would almost certainly develop breast cancer in their lifetime.
That’s why every breast-cancer patient, both women and men, diagnosed in Orange County since March 1 is being enrolled in a study that will look at the genes and the risk factors for breast cancer in their families.
The cancer database of the Cancer Surveillance Program of Orange County is an ideal resource for conducting population-based family studies under a National Cancer Institute study recently awarded to UC Irvine’s Epidemiology Program. More than 1,400 cases of breast cancer are diagnosed in Orange County each year.
The long-term objective of the NCI study is to characterize more precisely the risk factors and the clinical and molecular aspects of breast cancer. It will also be important to identify the individual hereditary breast cancer predisposing syndromes, in order to develop a more effective means of identifying high-risk families. This will lead to therapeutic decisions and cancer prevention measures that are designed to meet the special needs of each person, as well as contribute to a better understanding of cancer.
