Hormonal contraception has been available since the 1960s. Over the years, the dose of estrogen has been reduced and the type of progestin has been changed in the pills. According to a Centers for Disease Control and Prevention report that reviewed contraceptive use from 2006 to 2010, two thirds of reproductive-age women use some type of contraception, and 17% of them, mainly younger and unmarried women, use the oral contraceptive pill (OCP).
OCPs are associated with noncontraceptive benefits. These include reduced menstrual blood loss, less dysmenorrheal and premenstrual symptoms, and a lower incidence of ovarian cysts and certain types of cancer.
Estrogen and progesterone may influence cancer development and growth. This has been a concern ever since the introduction of hormonal contraception. This cohort study evaluated the impact of OCP use on cancer.
The study was initiated by UK general practitioners in 1968. Initially, 23,000 women using OCPs and 23,000 women with no past or current use of OCP were enrolled between 1968 and 1969. Data on OCP use, subsequent cancer diagnosis and further risk factors (smoking, social class, parity, significant medical history) were collected. Analysis was done for the entire cohort, as well as for subgroups (based on age categories and smoking).
Of the women who were ever users of OCP, 4661 were diagnosed with at least one cancer over 884,895 woman-years of follow up. Among the never-users, 2341 were diagnosed with cancer over 388,505 woman-years of follow-up.
The researchers also reported the following incidence rate ratios (IRRs) for cancer among ever-users versus never-users:
- Any type of cancer: 0.96; 99% confidence interval (CI), 0.90-1.03
- Colon/rectal cancer: 0.81; 99% CI, 0.66-0.99
- Endometrial cancer: 0.66; 99% CI, 0.48-0.89
- Ovarian cancer: 0.67; 99% CI, 0.50-0.89
- Breast cancer: 1.04; 99% CI, 0.91-1.17
- Lymphatic/hemopoetic cancer: 0.74; 99% CI, 0.58-0.94
Other findings included:
- Cancer risk increased with age and smoking in both groups.
- Current or recent (< 5 years) users of OCP were at an increased risk for cancer in general (IRR, 1.28; 99% CI, 1.08-1.54), breast cancer (IRR, 1.48; 99% CI, 1.10-1.97), and cervical cancer: (IRR, 2.32; 99% CI, 1.24-4.34)
- Increased cancer risk was no longer present among those with > 5 years since last use.
- Reduced risk for endometrial and ovarian cancer was seen in both recent users and past users, and the protective effective was still present among those with > 35 years since last use.
Researchers have long studied a possible association between cancer and OCP use. Certain cancers, mainly those of the female reproductive organs, are associated with reproductive factors, such as age at menarche or menopause, cycle regularity, and parity.[4,5,6,7]
Previous studies have found a slightly increased risk for breast cancer among current and recent users of OCPs.[4,5] This study has detected a similar association with no effect 5 years after discontinuation.
The risk for ovarian cancer is reduced when the number of ovulations is fewer and when transport of potentially carcinogen agents is reduced through the genital tract. OCPs have a beneficial effect on both of these mechanisms. Just like previous studies, this paper also reports reduced risk for ovarian cancer among current and past users of OCP. This effect seems to persist for many years.
There are many contraceptive options to choose from. When individual decisions and recommendations are made, the noncontraceptive benefits should also be discussed with the potential user.