The contraceptive pill and ovarian cancer risk

Overview: Cancer of the ovary affects more than 6,500 women in the UK each year. It is the fifth most common cancer among women after breast cancer, bowel cancer, lung cancer and cancer of the uterus (womb). Ovarian cancer is most common in women who have had the menopause (usually over the age of 45), but it can affect women of any age. It is well established that the use of oral contraceptives reduces the risk of ovarian cancer, but the associations with other reproductive variables are less clear. See the NHS Evidence topic page on ovarian cancer for a general overview of the condition.

Current advice: Oral contraceptives have been found to increase the risk of some cancers, and lower the risk of others. NICE recommends that women should not be prescribed the oral contraceptive pill purely for prevention of cancer. Women aged over 35 years with a family history of breast cancer should be informed of an increased risk of breast cancer associated with taking the oral contraceptive pill, given that their absolute risk increases with age. There is accredited guidance on combined hormonal contraception from the Faculty of Sexual and Reproductive Healthcare.

New evidence: A large prospective study, using data from the European Prospective Investigation into Cancer and Nutrition (EPIC), examined the associations of oral contraceptive use and reproductive factors with ovarian cancer risk (Tsilidis et al. 2011). Among 327,396 eligible women, 878 developed ovarian cancer over an average of 9 years. The results show that women who used oral contraceptives for 10 or more years had a 45% lower risk compared with users of 1 year or less. It is suggested that the dose of oestrogen contained in oral contraceptives has a negligible impact on the association with ovarian cancer risk. Having a child was linked to a 29% lower risk after the first child, with progressive lower risks with each additional full-term pregnancy. Age at menarche, age at first full-term pregnancy, incomplete pregnancies and breastfeeding were not found to be associated with risk. The researchers conclude that the study shows a strong protective association of oral contraceptives and parity with ovarian cancer risk. Commentary: “Many studies have shown the association between oral contraceptive use, pregnancy and reduced risk of epithelial ovarian cancer. This, the largest prospective study, confirms these findings and also reveals the increased risk associated with a late menopause. Equally, the duration of oral contraceptive use impacts on the protective effect, in that, the highest protection occurs with 10 years or more use. There is however, protection even with a single year usage. One action of combined oral contraceptives (like pregnancy), is the cessation of ovulation – which fits the long standing theory that a woman’s risk of ovarian cancer is proportional to the number of ovulatory cycles during her lifetime. However further research is required to identify what in fact is affording protection – cessation of ovulation alone or some other hormonal effect? In order to develop a proper preventative strategy these questions require addressing”. – Professor Sean Kehoe, Gynaecological Oncologist and President of the British Gynaecological Cancer Society.

 

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