Linda A. Webster

The independent associations of parity, age at first full term pregnancy, and duration of breastfeeding with the risk of breast cancer

Although the important influence of a womans reproductive history on her risk of breast cancer is widely recognized, it is not clear whether this is wholly accounted for by the age at her first full-term pregnancy, or whether there are additional, independent influences of breastfeeding or number of children. To examine the respective contributions to the risk of breast cancer of these reproductive factors, we used logistic regression methods to analyze data from a multicenter case-control study, the Cancer and Steroid Hormone Study. Included in the analysis were 4599 women, 20-55 years of age, identified as having an initial diagnosis of breast cancer by one of eight collaborating population-based cancer registries. The 4536 controls were women of similar ages selected by random dialing of households with telephones in the same eight areas. As expected, age at first full-term pregnancy exerted a strong influence on the risk of breast cancer. However, after it and other potentially confounding factors had been controlled for, parity and duration of breastfeeding also had a strong influence on the risk of breast cancer. Compared with women of parity one, women of parity seven or greater had an adjusted relative risk of breast cancer of 0.59 (95% CL, 0.44-0.79). Compared with parous women who never breastfed, women who had breastfed for 25 months or more had an adjusted relative risk of 0.67 (0.52-0.85). These results do not support the supposed preeminent importance of age at first full-term pregnancy among the reproductive determinants of breast carcinogenesis. Resolution of this issue may have important implications for elucidating hormonal influences on breast cancer and for projecting future trends in the disease.

The Reduction in Risk of Ovarian Cancer Associated with Oral-Contraceptive Use

Although several studies have reported that the use of oral contraceptives decreases the risk of ovarian cancer, it is not clear whether the effect varies according to the oral-contraceptive formulation or the histologic type of cancer. To characterize this association more fully, we used data from a case-control study, the Cancer and Steroid Hormone Study. From 1980 to 1982, 546 women 20 to 54 years of age with ovarian cancer were enrolled from eight population-based cancer registries. The controls were 4228 women selected from the same areas. Women who had used oral contraceptives had a risk of epithelial ovarian cancer of 0.6 (95 percent confidence interval, 0.5 to 0.7) as compared with those who had never used them. This protective effect was seen in women who had used oral contraceptives for as little as three to six months, and it continued for 15 years after use ended; it was independent of the specific oral-contraceptive formulation and of the histologic type of epithelial ovarian cancer. (We could not adequately assess the association with nonepithelial ovarian cancers because of an insufficient number of cases.) We conclude that the use of oral contraceptives decreases the risk of epithelial ovarian cancer.

Oral-contraceptive use and the risk of breast cancer. The cancer and steroid hormone study of the centers for disease control and the national institute of child health and human development

To investigate the effect of individual formulations of oral contraceptives on the risk of breast cancer in women, we analyzed case-control data from the Cancer and Steroid Hormone Study of the Centers for Disease Control. The cases were 4711 women 20 to 54 years old with newly diagnosed breast cancer who were selected from eight population-based cancer registries. The controls were 4676 women selected by random-digit dialing of the population of each area covered by a registry. As compared with women who had never used oral contraceptives, women who had used them had a relative risk of breast cancer of 1.0. Among women who used only one oral-contraceptive formulation, this estimate of relative risk did not change appreciably according to the formulation used. Neither the type of estrogen nor the type of progestin contained in oral contraceptives used was associated with an increased risk of breast cancer. The duration of oral-contraceptive use and the time since last use did not influence the risk. These findings provide further support for the contention that oral-contraceptive use does not increase the risk of breast cancer in women.

Endometrial cancer: How does cigarette smoking influence the risk of women under age 55 years having this tumor?

This analysis of the Cancer and Steroid Hormone Study, a multicenter, population-based case control investigation of hormone use by women of reproductive age and endometrial, breast, and ovarian cancer shows that cigarette smoking is not associated with either an increased or a decreased risk of endometrial cancer. This study included 437 women with endometrial cancer and 3200 control subjects, all of whom were between the ages of 20 and 54 years at the time of interview. The absence of any alteration of the risk of endometrial cancer and smoking was found consistently no matter which variable was used as a measure of smoking--ever or never smoked cigarettes, former or current smoking, light or heavy smoking, or age smoking began.

Prevalence and determinants of caesarean section in Jamaica.

The prevalence and determinants of primary caesarean section in Jamaica were estimated from a survey of women aged 14-49 years. Among 2328 women reporting 2395 live hospital births during the period January 1984 to May 1989, the prevalence of caesarean section was 4.1%. Repeat caesarean sections accounted for 1.3% of the hospital births during that period. Of the medical complications studied, prolonged labour and/or cephalopelvic disproportion carried the highest risks of primary caesarean section, followed by breech presentation, maternal diabetes, a high birth-weight baby, maternal hypertension, and a low birth-weight baby. The risk of primary caesarean section increased with maternal age, decreased with parity, was higher for urban than for rural residents, and was higher for births in private versus government hospitals.

Oral Contraceptives and Endometrial Cancer-Reply

ABSTRACT In Reply.— Dr Maxey has raised the issue of whether the results of the recently published study of endometrial cancer and oral contraceptives could possibly be biased because one needs a telephone to be selected as a control. He was concerned that women of upper socioeconomic status would be more apt to have telephones and also more apt to use oral contraceptives than those of lower socioeconomic status. If this were true, it would cause a spuriously high estimate of oral contraceptive use in our control group relative to our cases— cases being ascertained from hospital logs and therefore not needing telephones to enter the study. We were concerned about this possible bias and asked cases whether they had a telephone. In fact, 186 of the 187 cases had telephones. Thus, our method of selecting controls by telephone could not have biased the study in the way that Dr Maxey