Mayo Clinic Proceedings
Volume 83, Issue 7 , Pages 849-850, July 2008

Oral Contraceptives and Breast Cancer

Article Outline

 

To the Editor: In a Concise Review for Clinicians, Casey et al1 examine oral contraceptive (OC) use and the risk of breast cancer. It is noteworthy that the lead author is a consultant for Organon USA, maker of several OCs and other hormonal contraceptives; although Dr Casey disclosed this fact, a potential conflict of interest is nonetheless apparent. The authors conclude that “current evidence suggests that OCs do not play a clinically important role in the risk of breast cancer.” That overly broad and inaccurate statement does not reflect the existing literature on OCs and breast cancer. Specifically, the authors fail to discuss the known differences in the epidemiology and pathology between premenopausal and postmenopausal breast cancer, including the potential differences in risk of disease associated with OC use. Instead, they treat all breast cancers as the same. Casey et al further fail to discuss adequately the timing of OC exposure as it relates to the risk of premenopausal and postmenopausal disease.

Using data from 39 case-control studies conducted after 1980, we published in the October 2006 issue of Mayo Clinic Proceedings an analysis showing a link between OC use and premenopausal breast cancer (odds ratio, 1.19; 95% confidence interval, 1.09-1.29).2 This risk was greatest in women who used OCs for 4 or more years before a first full-term pregnancy (FFTP) (odds ratio, 1.52; 99% confidence interval, 1.19-1.93).

Casey et al minimize our work by stating that it is based on “older data with higher-dose estrogen and older progestin OC formulations.” This is inaccurate: in 34 of the 39 studies in our meta-analysis, 100% of the cases developed breast cancer during or after 1980. In the remaining 5 studies, most cases developed breast cancer after 1980. Hence, nearly all women in our meta-analysis developed breast cancer after 1980, when newer low-dose, triphasic OCs were more common. Moreover, recent data, including those in the Oxford study,3 show that low-dose OCs are associated with a greater risk of breast cancer than are high-dose regimens,4, 5 a point Casey et al overlooked by citing a single study from 2002 (which was included in our analysis) that showed no risk associated with OC use in general. The discussion section of our article reviews the potential links between newer OC formulations and breast cancer risk.

To support their conclusion, Casey et al cite the Oxford study.6 However, the Oxford analysis has various weaknesses that were never mentioned: (1) it included several older studies in which data were obtained before 1980, when women tended to use OCs for shorter lengths of time before FFTP3; (2) two-thirds of the breast cancer cases were women older than 45 years and thus likely to be postmenopausal7; and (3) no data were published for the risks in parous premenopausal women (or women <50 years) who took OCs before their FFTP. Therefore, the Oxford data cannot be generalized to all women, especially not to parous premenopausal women.

It is disappointing that an article aimed at providing clinicians with information to counsel their patients inaccurately and incompletely represents the established literature. Our work demonstrates that, contrary to the conclusion of the Casey et al article, current evidence does suggest that OCs increase the risk of breast cancer among premenopausal women. Notably, premenopausal women represent more than 20% of the newly diagnosed cases of breast cancer in the United States.8

Although the incidence rate of invasive breast cancer in postmenopausal women has sharply decreased since 2001, the rate among premenopausal women has remained steady.9 Moreover, premenopausal women often experience worse outcomes than postmenopausal women.9 While we agree with Casey et al that further research is needed to clarify the OC-breast cancer link, in the interim, we do not think it is fair to minimize or dismiss the potential risk of premenopausal breast cancer associated with OC use. Women deserve to be provided with the most accurate and up-to-date information on the potential risks associated with OCs so that they can make their own informed decisions. Their lives depend on it.

Back to Article Outline

REFERENCES 

  1. Casey PM , Cerhan JR , Pruthi S . Oral contraceptive use and the risk of breast cancer . Mayo Clin Proc . 2008;83(1):86–91
  2. Kahlenborn C , Modugno F , Potter DM , Severs WB . Oral contraceptive use as a risk factor for premenopausal breast cancer: a meta-analysis . Mayo Clin Proc . 2006;81(10):1290–1302
  3. Collaborative Group on Hormonal Factors in Breast Cancer  . Breast cancer and hormonal contraceptives: further results . Contraception . 1996;54(3, suppl):1S–106S Appendix 62.
  4. Breast cancer and combined oral contraceptives: results from a multinational study: WHO Collaborative Study of Neoplasia and Steroid Contraceptives . Br J Cancer . 1990;61(1):110–119
  5. Rookus MA , van Leeuwen FE , Netherlands Oral Contraceptives and Breast Cancer Study Group  . Oral contraceptives and risk of breast cancer in women aged 20-54 years . Lancet . 1994;344(8926):844–851
  6. Collaborative Group on Hormonal Factors in Breast Cancer  . Breast cancer and hormonal contraceptives: collaborative reanalysis of individual data on 53,297 women with breast cancer and 100,239 women without breast cancer from 54 epidemiological studies . Lancet . 1996;347(9017):1713–1727
  7. Althuis MD , Brogan DR , Coates RJ , et al.   Hormonal content and potency of oral contraceptives and breast cancer risk among young women . Br J Cancer . 2003;88(1):50–57
  8. American Cancer Society  . Breast Cancer Facts & Figures 2003-2004 . Atlanta, GA: American Cancer Society; 2003;
  9. American Cancer Society  . Breast Cancer Facts & Figures 2007-2008 . Atlanta, GA: American Cancer Society; 2007;

PII: S0025-6196(11)60925-7

doi:10.4065/83.7.849-a

Mayo Clinic Proceedings
Volume 83, Issue 7 , Pages 849-850, July 2008

Article Tools