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Oral Contraceptives and Cervical Cancer
Abstract & Commentary
By Alison Edelman, MD, MPH, Assistant Professor, Assistant Director of the Family Planning Fellowship Department of Obstetrics & Gynecology, Oregon Health & Science University, Portland, is Associate Editor for OB/GYN Clinical Alert
Dr Edelman reports no financial relationship to this field of study
Synopsis: The risk of cervical cancer is minimally increased (less than 1 additional case per 1,000 women) among current users of oral contraceptives but declines after cessation of use. This study does not provide evidence that oral contraceptives cause cervical cancer.
Source: International Collaboration of Epidemiological Studies of Cervical Cancer. Lancet. 2007;370:1609-1621.
The Collaborative Group on Epidemiological Studies of Cervical Cancer has combined and reanalyzed any relevant data from all epidemiological studies on the association between cervical carcinoma and the pattern of oral contraceptive use.1 The risk of cervical cancer was increased in current oral contraceptive (OC) users with increasing duration of use [relative risk for 5 or more years' use vs never use 1.90 (95% CI 1.69-2.13)]. After OC cessation, the risk declines and is equal to that of never users at 10 years. When adjusting for potential confounders, in particular age at first intercourse and number of sexual partners, the relative risk of invasive cervical cancer in current OC users decreased to 1.05 (95% CI 1.04-1.07). Although based on limited numbers, high-risk HPV infection was not significantly associated with ever-use of OCs or use for 5 years or greater [RR 1.19 (95% CI 0.92-1.52)].
Unfortunately, the most important implication of a study like this (birth control is incredibly safe) is not the one that is publicized by the media (birth control causes cancer). This study did not demonstrate that OCs cause cervical cancer and is not a study that can establish causation. This study found a very small risk of cervical cancer associated with OC use.1 The findings in this study are no surprise given that several previous articles have found a similarly small risk of cervical cancer associated with OC use.2,3
Now, what kind of risk are we talking about? A relative risk of 1.0 translates to no difference in risk between two groups being studied.4 This study found a small but statistically significant risk of cervical cancer associated with OC use (RR = 1.9) but after adjusting for confounders (ie, age, age at first partner, number of partners, smoking status) this risk decreased to 1.05.1 Just because something is statistically significant doesn't mean that it's clinically significant! To put these numbers in perspective, a relative risk of 1.9 translates to less than one additional case of cervical cancer per 1,000 women. To really put this in perspective, the relative risk of lung cancer with tobacco use is 10.7 and has been shown to be the cause of about 87% of lung cancers.5
Thus, the findings of this study should, overall, be reassuring to you in its confirmation of a weak and non-persistent association of OCs and cervical cancer. Instead, we can use this as an opportunity with patients to discuss cervical cancer prevention and early detection. HPV infection is a known cause of cervical cancer. We have two very effective tools to prevent HPV infection— the HPV vaccine and condoms. In addition, regular PAP screening can detect and allow treatment of precancerous lesions.
Finally, remember to focus on the forest rather than the trees. Not to diminish the seriousness of cervical cancer, but unintended pregnancy rates are at epidemic levels in the United States (approximately 50%) and internationally, pregnancy is a major cause of maternal morbidity and mortality.6,7 Misinterpretation and exaggeration of scientific results by the media in regard to birth control have been shown to directly influence rates of unintended pregnancy by scaring women to discontinue their birth control ("Pill Scare of 1995") when in reality, OCs have been well-studied and are extremely safe.8,9 OCs provide women with a multitude of health benefits beyond contraception including prevention of ovarian and endometrial cancer.10-13