Oral contraceptives and breast cancer: a national study

In a population based case-control study 433 New Zealand women aged 25-54 with newly diagnosed breast cancer were compared with 897 women selected at random from the electoral rolls. The relative risk of breast cancer in women who had ever used oral contraceptives was 0.94 (95% confidence interval 0.70 to 1.25). The relative risk in women aged 25-34 at diagnosis was estimated to be 2.2 (95% confidence interval 0.47 to 9.9) and in older women less than 1. Analyses of risk by duration of use of oral contraceptives, age at first use, and time since first use showed no adverse effect of the pill. In particular, there was no increased risk in women who had used oral contraceptives before the age of 25 or before their first pregnancy, even for prolonged periods. Given the high prevalence of use in New Zealand, this study provides strong evidence against the hypothesis that use of oral contraceptives at young ages increases the risk of breast cancer.     

Oral contraceptives and breast cancer. A prospective cohort study

In 1976, information on oral contraceptive (OC) use as well as numerous risk factors for breast cancer was provided by 121,964 married female registered nurses aged 30 to 55 years. Ninety-two percent of women in the cohort completed follow-up questionnaires, and vital records were systematically searched to ascertain deaths among nonrespondents. After four years of follow-up, 592 incident cases of breast cancer were identified. Compared with never users, the age-adjusted relative risk (RR) of breast cancer, regardless of menopausal status, among all women who had ever used OCs was 1.0. Among premenopausal women compared with those who had never used OCs, the RR of breast cancer was 1.5 for current use of OCs in 1976 and 1.0 for past use. Among postmenopausal women, the RR for past use of OCs was 1.0. These estimates were essentially unaltered after controlling for other known risk factors for breast cancer in multiple logistic regression analysis. Furthermore, there was no modification of these effects by family history of breast cancer, age at first use, timing of the first birth, or other breast cancer risk factors. Data on past use of OCs provide substantial reassuring evidence that there is no large excess risk of breast cancer within a few years of cessation of pill use. The observed moderate elevation of breast cancer risk with current use was of borderline statistical significance. However, the observation was based on 29 cases and may reflect the effect of sampling variability, as most other studies have not observed a relationship between current use of OCs and breast cancer in women of this age.     

Oral contraceptives may tend to protect against benign breast cancer

A retrospective epidemiological study was made of all women of reproductive age admitted to 5 London hospitals for primary treatment of breast cancer or biopsy of a mass in the breast. The only significant difference was that the benign disease group had used oral contraceptives about half as long as the controls. 12% of the women with benign breast lesions used oral contraceptives the month immediately preceding discovery of the breast mass. 22% of the Controls used the contraceptives during the corresponding month.     

Oral contraceptives and cervical cancer risk in Costa Rica. Detection bias or causal association?

To examine the relationship between cervical cancer and oral contraceptive (OC) use, we analyzed data from a population-based, case-control study in Costa Rica. Women aged 25 to 58 years in whom cervical cancer was diagnosed and reported to the National Tumor Registry were examined as two separate case groups: invasive cervical cancer and carcinoma in situ (CIS). Controls were women aged 25 to 58 years identified through a national survey. Women who had used OCs had no increased risk of invasive cervical cancer compared with women who had never used OCs (relative risk, 0.8; 95% confidence interval, 0.5 to 1.3). Women who had used OCs had an increased risk of CIS compared with those who had never used OCs (relative risk, 1.6; 95% confidence interval, 1.2 to 2.2). However, further analyses indicated that this increased risk was confined to those who had recently used OCs. Also, the risk of CIS was not elevated in subgroups in which a history of cervical smears was not strongly linked to OC use. The elevated risk of CIS among OC users may therefore reflect a bias caused by enhanced detection of disease rather than a causal association.     

Oral contraceptives and hepatocellular carcinoma

A series of 26 white women aged under 50 who developed hepatocellular carcinoma in a non-cirrhotic liver were studied for the possible role of oral contraceptives. Eighteen of the women had used the "pill" for a median of eight years. Over 1300 women whose use of the pill had been determined in another study served as controls. Patients and controls were divided into five age and four calendar groups and the relative risks associated with oral contraceptives calculated by multivariate analysis. Short term use of the pill was not associated with an increased risk of tumour development; nevertheless, use for eight years or more was associated with a 4.4-fold increased risk (p less than 0.01). When patients with markers of hepatitis B virus infection were excluded the relative risk was 7.2 (p less than 0.01). In both instances the absolute risk for developing hepatoma remained low.     

Oral contraceptives and blood pressure

Both cross-sectional and longitudinal analysis of data from 13,358 women showed that oral contraceptive use is associated with a slight but statistically significant (P lesser than .05) rise in mean blood pressure, which is reversible. The age-adjusted proportion of oral contraceptive users with a blood pressure over 140/90 mm Hg was about three times that on nonusers. These findings are caused by a uniform upward shift in the blood pressure distribution of oral contraceptive users compared to nonusers. Women continuing oral contraceptive use had no appreciably greater change in blood pressure between two visits than persistent nonusers. The clinical implications of a mild contraceptive-induced blood pressure elevation (systolic, 5 to 6 mm Hg; diastolic, 1 to 2 mm Hg) remain unsettled but disturbing.