Other Studies

Several studies have found no association between hormonal contraceptive use and breast cancer. A case-control study conducted by the US Centers for Disease Control and Prevention, for example, found an RR of 1.0 (95% CI, 0.8-1.3) among current oral contraceptive users compared with nonusers.6 This study included 4575 cases and 4682 controls aged 35 to 64.

Dr Grimes highlighted that this study was specifically designed to answer the question of breast cancer risk with oral contraceptive use, whereas the Danish administrative database was not. Yet, in an editorial, David J. Hunter, MBBS, ScD, noted that “owing to the age range of the women involved in that study (35 to 64 years), almost all use of oral contraceptives was among women who had used them in the past.”3

Clinical Applicability

Hormonal contraception is used by an estimated 140 million women worldwide, or about 13% of women aged 15 to 49, and is highly effective at preventing unwanted pregnancy, as well as treating conditions such as dysmenorrhea or menorrhagia.1,3 Hormonal contraception has also been associated with reductions in the risk of other cancers, including ovarian, endometrial, and colorectal. The benefits of hormonal contraception, therefore, must be balanced with the potential small risk of breast cancer.

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Dr Hunter highlighted in his editorial that these findings must also be viewed in context of the low rates of breast cancer among younger women — the women who are most likely to be using hormonal contraception. “The absolute increase in risk is 13 per 100,000 women overall, but only 2 per 100,000 women younger than 35 years of age; most of the cases that occurred in this analysis occurred among women who were using oral contraceptives in their 40s,” he wrote.

There is no evidence that women at high risk of breast cancer, such as those who harbor BRCA1 or BRCA2 mutations, should avoid hormonal contraception. Dr Lidegaard noted that “as these women at the same time have an increased risk of ovarian cancer, against which also newer combined hormonal contraceptives protect, I recommend combined products rather than progestin-only products…then regular breast examinations.”

References

  1. Mørch LS, Skovlund CW, Hannaford PC, Iversen L, Fielding S, Lidegaard Ø. Contemporary hormonal contraception and the risk of breast cancer. N Engl J Med. 2017;377:2228-39. doi: 10.1056/NEJMoa1700732
  2. Brisken C, Hess K, Jeitziner R. Progesterone and overlooked endocrine pathways in breast cancer pathogenesis. Endocrinology. 2015;156:3442-50. doi: 10.1210/en.2015-1392
  3. Hunter DJ. Oral Contraceptives and the small increased risk of breast cancer. N Engl J Med. 2017;377:2276-7.
  4. Grimes DA, Schulz KF. False alarms and pseudo-epidemics. Obstet Gynecol. 2012;120:920-7. doi: 10.1097/AOG.0b013e31826af61a
  5. Grimes DA. Epidemiologic research using administrative databases: garbage in, garbage out. Obstet Gynecol. 2010;116:1018-9.
  6. Marchbanks PA, McDonald JA, Wilson HG, et al. Oral contraceptives and the risk of breast cancer. N Engl J Med. 2002;346:2025-32.