Hormones and cancer in the UK - statistics

Hormone levels may explain differences in risk for some of the most commonly diagnosed female cancers and could be responsible for as many as 15% of cancer deaths in the UK 1.

 

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Summary

The lifestyle choices that determine hormone levels are not as straightforward as stopping smoking or eating healthily and are largely dictated by reproductive or genetic factors, over which individuals may have little or no control.

Table 5.1 shows a summary of what we know about hormones and cancer risk.

Table 5.1: Exogenous hormones summary box

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Endogenous hormones and cancer risk

The most recent worldwide reanalysis of 18 prospective studies showed no association between levels of endogenous sex hormones and risk of prostate cancer overall. 2

Risk of ovarian, endometrial and breast cancers increases with earlier age at menarche and later menopause, and reduces with each full-term pregnancy (the first full-term pregnancy providing more protection than successive ones). 3, 4 There is a transient increase in risk of breast cancer with each full-term pregnancy after the age of 25, and this is most marked with a woman’s first pregnancy. Uniparous women with a first full-term pregnancy after the age of 30 have a higher breast cancer risk than childless women until their late 50s. 5

The total fertility rate (average number of children per woman) in women in England and Wales in 2009 was 2.0, which is similar to the mid-1970s, but lower than the mid-1960s, when it was almost 3.16

Breast cancer risk is reduced by around 4% for each year a woman breastfeeds 4. Evidence for a protective effect against ovarian cancer is mixed. 6,17,18 The European Prospective Investigation into Cancer showed no effect of breastfeeding on endometrial cancer risk.7 According to the latest survey, around 76% of mothers in the UK breastfeed initially, compared with 62% in the 1990s, but only 34% of women breastfeed for more than four months and only a quarter for more than six months. 8

A study published in December 2011 estimated that around 3% of breast cancers and almost 18% of ovarian cancers (equivalent to around 1.7% of all cancers in women in the UK) are linked to women breastfeeding their children for less than six months.22

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Oral contraceptives and cancer

A meta-analysis of European case-control studies indicates that use of OCs for five or more years results in a 50% reduction in risk of ovarian cancer which remains for more than 20 years. 9 Case-control studies have consistently reported a 40 to 60% reduction in risk of endometrial cancer, increasing with duration of use, among users of combination OCs. 10 There is a slight transient increase in risk of breast cancer while OCs are taken. 11, 12

Use of OCs for more than five years results in a duration-dependent increased risk for cervical cancer after adjustment for potential confounders including human papillomavirus (HPV) status (see infections section below), smoking and use of barrier contraceptives. Risk falls once use of OCs is stopped. 13

A study published in December 2011 estimated that there were around 1,600 fewer cases of cancer in the UK in 2010 than there would have been without use of OCs, due to their protective effect against ovarian and womb cancer, which outweighed the increased risk of breast and cervical cancers.23

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Hormone replacement therapy and cancer

Women taking oestrogen-only hormone replacement therapy (HRT) are at an increased risk of endometrial and ovarian cancers. 14 The risk of uterine cancer is approximately doubled after five years, while the risk of ovarian cancer increases by about 25% for the same duration of use. 3, 10 Combined oestrogen-progestagen HRT increases risk of ovarian cancer by a smaller amount.19 Risk of uterine cancer is slightly increased in women using cyclic-combined HRT, but slightly reduced in those using continuous-combined HRT. 20

The UK ‘Million Women Study’ reported breast cancer RRs for current use of oestrogen-progestagen therapy or oestrogen only of 2 and 1.3, respectively. Risk increased with duration of use, with risk ratios of 2.3 for 10 or more years of combined HRT, compared with 1.5 for less than one year. There was a marginally increased risk in women who stopped HRT less than a year before entering the study, but no difference in risk between never users and women as a group who stopped therapy at some point in the previous five years. 15

In the UK, use of HRT peaked in 2000-01, when approximately 25% of women aged 45-69 were using it. The percentage had fallen to half that by 2006. It has been estimated that, in 2005, there were 1,400 fewer cases of breast cancer in women aged 50-59 in the UK than there would have been if use had not fallen. 21 Nonetheless, a study published in December 2011 estimated that around 1,500 cases of breast cancer in the UK in 2010 were linked to use of HRT, in addition to around 100 womb cancers and 50 ovarian cancers (equivalent to around 1% of all cancers in women in the UK). 23

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References for hormones and cancer risk

  1.  Doll, R. and P.J. Fau, Epidemiology of Cancer, in Oxford Textbook of Medicine. 4th ed, D. Warrell, et al., Editors. 2003, OUP.
  2.  Roddam, A.W., Allen, N.E., Appleby, P., Key, T.J. Endogenous sex hormones and prostate cancer: a collaborative analysis of 18 prospective studies. J Natl Cancer Inst, 2008. 100(3): p. 170-83.
  3.  Pike, M.C., C.L. Pearce, and A.H. Wu, Prevention of cancers of the breast, endometrium and ovary. Oncogene, 2004. 23(38): p. 6379-91.
  4.  Collaborative Group on Hormonal Factors in Breast Cancer, Breast cancer and breastfeeding: collaborative reanalysis of individual data from 47 epidemiological studies in 30 countries, including 50302 women with breast cancer and 96973 women without the disease. Lancet, 2002. 360(9328): p. 187-95.
  5.  Albrektsen, G., et al., Breast cancer risk by age at birth, time since birth and time intervals between births: exploring interaction effects. Br J Cancer, 2005. 92(1): p. 167-75.
  6.  Danforth, K.N., Tworoger, S.S., Hecht, J.L. et al., Breastfeeding and risk of ovarian cancer in two prospective cohorts. Cancer Causes Control, 2007. 18(5): p. 517-23.
  7.  Dossus, L., Allen, N., Kaaks, R., et al,, Reproductive risk factors and endometrial cancer: the European Prospective Investigation into Cancer and Nutrition. Int J Cancer, 2010. 127(2): p. 442-51.
  8.  Bolling,K. et al. Infant Feeding 2005. The Information Centre: 2007.
  9.  Bosetti, C., et al., Long-term effects of oral contraceptives on ovarian cancer risk. Int J Cancer,2002. 102(3): p. 262-5.
  10.  Schottenfeld D and Fraumeni J, Cancer Epidemiology and Prevention. 1996, Oxford: Oxford University Press.
  11.  Boyle, P., et al., European Code Against Cancer and scientific justification: third version (2003). Ann Oncol, 2003. 14(7): p. 973-1005.
  12.  Collaborative Group on Hormonal Factors in Breast Cancer, Breast cancer and hormonal contraceptives: collaborative reanalysis of individual data on 53297 women with breast cancer and 100239 women without breast cancer from 54 epidemiological studies. Collaborative Group on Hormonal Factors in Breast Cancer. Lancet, 1996. 347(9017): p. 1713-27.
  13.  Smith, J.S., et al., Cervical cancer and use of hormonal contraceptives: a systematic review. Lancet, 2003. 361(9364): p. 1159-67.
  14.  Lacey, J.V., Jr., et al., Menopausal hormone replacement therapy and risk of ovarian cancer. Jama, 2002. 288(3): p. 334-41.
  15.  Beral, V., Breast cancer and hormone-replacement therapy in the Million Women Study. The Lancet, 2003. 362(9382): p. 419-427.
  16.  Office for National Statistics, Live births: Fertility rates fall. 2010.
  17.  Chiaffarino, F., Breastfeeding and the risk of epithelial ovarian cancer in an Italian population. Gynecol Oncol, 2005. 98(2): p. 304-8.
  18.  Titus-Ernstoff, L., Rees, J. R., Terry, K.L., Cramer, D.W., Breast-feeding the last born child and risk of ovarian cancer. Cancer Causes Control, 2009. 21(2): p. 201-7.
  19.  Pearce, C. L., Chung, K., Pike, M.C., Wu, A.H., Increased ovarian cancer risk associated with menopausal estrogen therapy is reduced by adding a progestin. Cancer, 2009. 115(3): p. 531-9.
  20.  Beral, V., Bull, D., Reeves, G., Endometrial cancer and hormone-replacement therapy in the Million Women Study. Lancet, 2005. 365(9470): p. 1543-51.
  21.  Parkin, D.M, Is the recent fall in incidence of post-menopausal breast cancer in UK related to changes in use of hormone replacement therapy?. Eur J Cancer, 2009. 45(9): p. 1649-53.
  22.  Parkin, D.M. Cancers attributable to reproductive factors in the UK in 2010. Br J Cancer, 6 Dec 2011; 105 (S2):S73-S76; doi: 10.1038/bjc.2011.488
  23.  Parkin, D.M. Cancers attributable to exposure to hormones in the UK in 2010. Br J Cancer, 6 Dec 2011; 105 (S2):S42-S48; doi: 10.1038/bjc.2011.483