Researchers assessed associations between the duration of oral contraceptive use and ovarian, endometrial, breast, and colorectal cancer risk and whether these associations were modified by certain modifiable lifestyle factors.
Long-term use of oral contraceptives (OC) is associated with reduced risk for ovarian and endometrial cancer, according to a study published in JAMA Oncology.
With the prominent use of OC in the US, there is continual research into their potential benefits and harms in relation to cancer. In 2013, the Agency for Healthcare Research and Quality released a report on “Oral Contraceptive Use for the Primary Prevention of Ovarian Cancer,” which integrated findings from published literature on OC use and risks of several cancers.
However, according to the authors of the study: “Data gaps were identified, including a need to understand OC-associated cancer risks in subpopulations, such as those stratified by smoking, obesity, or family history of cancer.” To address the gap, the authors examined the associations between the duration of OC use and ovarian, endometrial, breast, and colorectal cancer risk and whether these associations were altered by certain modifiable lifestyle factors.
The authors used the large prospective NIG-AARP Diet and Health Study, which enrolled patients from 1995 to 1996. Approximately 3.5 million members between age 50 and 71 were mailed a baseline questionnaire. The questionnaire inquired about duration of OC use, demographic characteristics, and health and lifestyle history, including current smoking status, alcohol use, body mass index (BMI), and physical activity. Participants were also asked about family history of breast and colon cancers. Six months following the baseline questionnaire, a questionnaire on family history of ovarian cancer was sent out. More than 100,000 women were included in the study.
Long-term OC use was associated with a 40% reduction in cancer risk (HR, 0.60; 95% Cl, 0.47-0.76; P <.001). For smokers, long-term OC use reduced the risk by 30% (former smokers) to 66% (current smokers). Increasing the duration of OC use was also associated with a reduced risk among women with BMIs under 25, women not consuming alcohol, and women consuming 2 servings of alcohol per day or less.
For endometrial cancer, long-term OC use reduced the risk by 34% (95% Cl, 0.56-0.78; P <.001). The strongest risk reduction was seen in current smokers (long-term use HR, 0.47; 95% CI, 0.25-0.88; P  =.002). While there were no reduced risks for endometrial cancer associated with OC use among women with BMIs of 25 or less, there was a reduced risk among women with BMIs of 30 or greater (long-term OC use: HR, 0.36; 95% CI, 0.25-0.52; P  < .001). There were also risk reductions in women consuming alcohol and those who exercised.
There were no associations observed in long-term OC use and breast cancer across the majority of the modifiers, but there were some associations of a slight increase of risk, according to the authors. Long-term OC users who were current smokers had an increased risk of breast cancer (HR, 1.21; 95% CI, 1.01-1.44), as did moderate drinkers (HR, 1.08; 95% CI, 1.00-1.17; P = .05).
“Our identification of risk reductions for ovarian and endometrial cancer across most modifiable lifestyle factors suggests that OC use is beneficial for chemoprevention for a range of women with differing baseline risks for these cancers,” concluded the authors.