Association Of Breast Cancer Risk Research Articles

Breast Cancer Risk and Oral Contraceptive Use

The association between oral contraceptive use and breast cancer risk was examined using data from a case-control study of breast cancer in Long Island, New York. Cases were defined as female residents of Nassau and Suffolk Counties between the ages of 20 and 79, diagnosed with breast cancer between January 1, 1984 and December 31, 1986. Age- and county-matched controls were selected from driver's license files. Among all women under age 70 at diagnosis, there was no association between oral contraceptive use and breast cancer; there was, however, a positive association in the subgroup ages 20-49 (adjusted odds ratio = 1.68, 95% CI: 1.16-2.42). Risk increased with increasing duration of use, but did not differ between women who first used oral contraceptives before the first pregnancy and those who first used them later, or between women who first used oral contraceptives before age 25 and those who first used them at a later age. Risk also appeared to increase with number of years of use before the first pregnancy or before age 25, although numbers were small. History of benign breast disease did not influence risk. The association of breast cancer risk with oral contraceptive use appeared stronger in women from Suffolk County than Nassau County.

Dimethylbenzanthracene-induced mammary tumorigenesis in ethanol-fed rats

Epidemiological evidence indicates that ingestion of alcoholic beverages is a risk factor or is associated with a risk factor for breast cancer. A small increase in relative risk (1.1–1.2) compared to non-drinkers, has been reported for drinkers of small amounts of alcohol, approximately 3–4 drinks per week; a larger increase in relative risk (1.4–1.7) with a significant dose relationship occurs at intakes of 2–3 drinks per day. Two drinks per day would supply approximately 7–10% of a woman's caloric intake. This evidence, coupled with the general association of breast cancer risk with higher economic, nutritional and education status, supports the view that relevant animal models for study of the relationship between alcohol and breast cancer should employ moderate alcohol and good nutrient intake. Two carcinogenesis experiments were performed in ethanolfed, female, Sprague-Dawley rats. In the first, groups of 50 rats were fed control diet ad libitum (CON) or were fed the diet with 20% of calories supplied as ethanol (ETOH) or intake of ETOH rats (PF). They were given 7, 12-dimethylbenzanthracene (DMBA), 20 mg/kg, by gavage at 55 days of age and monitored for tumor development. There was no detectable effect of ethanol on mammary tumor latency, incidence, number, weight or histology. In the second experiment, rats divided into the same groups were given 25% and the dose of DMBA was increased to 30 mg/kg. Again, there was no detectable effect of ethanol on mammary tumorigenesis. Thus, no effect of ethanol on mammary gland tumorigenesis by DMBA was observed in rats treated by 2 different protocols.

THE ASSOCIATION OF AGE AND FAMILIAL RISK IN A CASE-CONTROL STUDY OF BREAST CANCER

To investigate the association of breast cancer risk, age, and family history of breast cancer, 779 breast cancer patients and 1,558 comparably aged control patients without cancer or a history of cancer were studied. All patients were admitted to Roswell Park Memorial Institute, Buffalo, New York between 1982 and 1987. After adjustment for the effects of other major breast cancer risk factors, no overall increase in risk for a history of breast cancer in a first-degree relative was observed among younger women. However, when the age at reported occurrence of breast cancer was considered, increased relative risk (RR) was observed when the affected first-degree relative was diagnosed at a young age (RR = 1.3). In contrast, among older patients, greater risk (RR = 1.9) was associated with diagnosis in a first-degree relative at an older age. Among patients aged 55 years or older, risk for reporting one first-degree relative with breast cancer was significant (RR = 1.8) and was greater when more than one first-degree relative was reported to have breast cancer (RR = 3.3). Bilaterality in an affected first-degree relative was associated with increased risk only among older patients (RR = 2.3). Other studies have observed various age-related effects, but the present research differs in that the authors studied both the age of the patient at risk and the age of the affected relatives across the full range of ages at which breast cancer occurs. These findings may have implications for the identification of populations for earlier initiation of routine screening and for laboratory investigation of the genetic etiology of breast cancer.

Association of Breast Cancer Risk With Age at First and Subsequent Births: A Study in the Population of the Estonian Republic<xref ref-type="fn" rid="fn2">2</xref>

Information on reproductive history was obtained from 362 urban breast cancer patients attending the oncological dispensaries at Tallinn and Tartu, Estonian Republic, and from 694 urban women participating in gynecologic screening programs offered by the same centers. The 2 groups were compared by means of Mantel-Haenszel and logistic regression procedures to estimate age-adjusted odds ratios. Women whose first birth occurred before 20 years of age had a breast cancer risk less than one-third the risk of nulliparous women. Risk increased with increase in age at first birth (AFB) but remained below 1.0 (relative to nulliparae), even in the highest AFB categories. The fertility rate in Estonia during the period of this study was relatively low, which facilitated an evaluation of the effect of births subsequent to the first. After adjustment for AFB, it appeared that in this population subsequent births had a protective effect additional to that conferred by the first birth. Moreover, for women who had only 2 children, the age at the time of birth of the second child was a determinant of that effect. Compared to nulliparous women, the breast cancer odds ratio for uniparous women who had their child before age 25 was 0.62, and the ratio for duoparous women who had both their children under that age was 0.18. Neither lactation nor menarche was a risk factor for breast cancer in this pouplation.

Age at menarche, probability of ovulation and breast cancer risk.

An analysis is undertaken of the frequency of ovulation in 17 groups of women aged 15 to 19 who had been the subjects of other studies. A urine specimen of at least 8 h accumulation had been provided on the 20th or 21st day of a menstrual cycle by 681 women. Analysis is restricted to 431 specimens which had been collected between 11 and 3 days prior to the onset of the subsequent menstrual period. A pregnanediol concentration of less than 1 mg per litre in such a specimen was taken as evidence that the cycle was anovular. The probability of a cycle being anovular was inversely and significantly related to the number of years since menarche, and, with years since menarche held constant, was positively but not significantly associated with age at menarche. This observation indicates that women with early menarche do not have a longer duration of exposure to anovular cycles than do those whose menarche is delayed, and that variation in the duration of exposure to post-menarcheal anovular cycles does not explain the association of breast cancer risk with early age at menarche. The 17 groups of women were classified into four categories according to ethnic origin and breast cancer incidence in the populations from which they derived. Anovular cycles were not more common in the high-risk groups; indeed, the two centers in the lowest risk category had the highest proportion of anovular cycles.

Risk factors of breast cancer in Burma.

A hospital-based case-control study of breast cancer was undertaken in Rangoon. The age-standardized incidence rate, 25.1 per 100,000 woman-years and the shape of the age-incidence curve show that Rangoon women have an intermediate level of breast cancer risk compared to women of other countries in the world. The analysis is based on 193 cases and 400 controls. Breast cancer risk was found to be directly related to educational attainment. There was an increased risk associated with early menarche and late menopause. The most striking finding was the strong inverse relationship between risk and parity; women who had six or more children have only one-third the breast cancer risk of married women who had less than four children. This association is not confounded by case-control differences in age at birth of first child. The association of breast cancer risk with age at first birth was not striking; only women with a first birth after age 30 were at increased risk. Breast cancer risk was unrelated to lactation. Overall, the epidemiology of breast cancer in Burma is similar to that in most other countries. However, the possibility of an unusual relationship of risk to parity and age at first parturition warrants further exploration.

Cohort fertility and increasing breast cancer incidence.

The question of whether the increase in breast cancer incidence in England and Wales and in Connecticut can be explained by a decrease in the fertility of cohorts of women in whom the breast cancer increase has been recorded is examined. Total reproductive performances were calculated for women born between 1841-1906. Those for whom data are complete up to the age of 45 showed diminished reproductive performance. Hover incomplete data for those born since 1906 indicate that there has been a rise in fertility along with an increase in breast cancer incidence. This implies that the previous decreased fertility changes were not responsible for the earlier breast cancer increase. In Connecticut in all age groups birthrates decreased regularly between 1917-1935. Thereafter birthrates increased except in the 40-44 age group. That frequent or prolonged lactation may reduce breast cancer risk has been considered as an explanation for the low breast cancer rates found in Japan and for the positive association of breast cancer risk with socioeconomic status. In the areas considered the frequency of breast-feeding has decreased in recent years. Therfore despite the recorded increase in fertility the total lactational experience is less than in earlier years. From these observations it is concluded that fertility changes do not explain the observed changes in breast cancer rates.