Following the dramatic fall in postmenopausal hormone therapy (HT) after the Women’s Health Initiative (WHI) publications in 2002/2003, a large number of papers have reported a 7% decline in breast cancer incidence in the USA and other countries. In a recent study [1], breast cancer incidence rates among non-Hispanic (NH) white women from 2003 to 2007 were evaluated. Data were obtained from the 12 Surveillance, Epidemiology, and End Results (SEER) registries (representing only 14% of the US population) for 2000–2007 by age and estrogen receptor (ER) status (ER+ or ER-). Prevalence of HT use was calculated using National Health Interview Survey data from 2000, 2005 and 2008. When a linear trend was fitted to the data from 2003 to 2007, there was no significant change (p = 0.46) in the incidence rate for ER+ breast cancers among NH white women. NH Black and Hispanic women did not experience the steep drop in incidence from 2002 to 2003 and there were no significant changes in incidence rates from 2003 to 2007. However, the incidence rate in NH white women aged 60–69 years increased by 4.8% from 2003 to 2007. ER- breast cancer incidence decreased in NH white women and black women except in the group aged 60–69 years. Use of HT has fallen from 22% in 2000 for NH white women aged 50–59 years to 4.8% in 2008 and from 12.9% in 2000 for NH white women aged 60–69 years to 3% in 2008. But, if HT use was lower in black women (7% to 1.2% in the age group 50–59 years), in NH white women the use of HT also fell from 18% to 1.4% in women aged 50–59 years.

Comment
This paper brings new interesting data about the fluctuation in breast cancer incidence following the decline of HT use in the USA. Most of the papers have argued for causality between cessation of HT and decrease of breast cancer incidence. However, as we have discussed in a previous publication [2], if the promoter effect of HT on the growth of a pre-existing cancer can play a part in the fluctuation of the incidence observed, other factors may have also played a role, such as decrease in screening adherence, screening saturation effect or variation in other risk factors. The results of this paper [1]show that, despite a continuous decrease in HT use over the time with an extremely low proportion of women still using HT in 2008, a stabilization of the incidence and even a re-increase in the incidence in women 60–69 years old were observed. This suggests that the decrease of incidence might be predominantly due to underdiagnosis of women who, because of stopping HT, did not have any more mammograms and clinical surveys. It is also suggested that some of the tumors were growing slowly and that stopping HT may have postponed their diagnosis. It is extremely likely that the re-increase observed in 60–69-year-old women is due to cancer which should have been diagnosed before if these women were still using HT. The stages of these cancers are not known and could be higher. A further interesting observation in this paper is that, in Hispanic white women, despite a pattern of HT use similar to that in NH white women, no modification in ER+ breast cancer incidence was observed. This could be due to lower numbers in this category but also argues for a more complex effect on breast cancer incidence than only the decline in HT use. Furthermore, two other papers have also reported a re-increase in breast cancer incidence in Canada after 2006 [3] and in a screening cohort from the USA [4].

Anne Gompel
Unité de Gynécologie-Endocrinienne, APHP, Hôtel-Dieu Hospital and University Paris Descartes, France

References
1. DeSantis C, Howlader N, Cronin KA, et al. Breast cancer incidence rates in US women are no longer declining. Cancer Epidemiol Biomarkers Prev 2011;20:733-9.
http://www.ncbi.nlm.nih.gov/pubmed/21357727
2. Gompel A, Plu-Bureau G. Is the decrease in breast cancer incidence related to decrease in postmenopausal hormone therapy? Ann NY Acad Sci 2010;1205:268-76.
http://www.ncbi.nlm.nih.gov/pubmed/20840283
3. De P, Neutel CI, Olivotto I, Morrison H. Breast cancer incidence and hormone replacement therapy in Canada. J Natl Cancer Inst 2010;102:1489-95.
http://www.ncbi.nlm.nih.gov/pubmed/20864685
4. Farhat GN, Walker R, Buist DSM, Onega T, Kerlikowske K. Changes in invasive breast cancer and ductal carcinoma in situ rates in relation to the decline in hormone therapy use. J Clin Oncol 2010;28:5140-6.
http://www.ncbi.nlm.nih.gov/pubmed/21060026