Journal of the National Cancer Institute Advance Access originally published online on April 8, 2008
JNCI Journal of the National Cancer Institute 2008 100(8):599; doi:10.1093/jnci/djn081
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Published by Oxford University Press 2008.
CORRESPONDENCE |
Response: Re: Declines in Invasive Breast Cancer and Use of Postmenopausal Hormone Therapy in a Screening Mammography Population
Affiliations of authors: Department of Epidemiology and Biostatistics and General Internal Medicine Section, Department of Veterans Affairs, University of California, San Francisco, CA (KK); Group Health Center for Health Studies, Seattle, WA (DSMB, RW, DLM); Department of Biostatistics, University of Washington, Seattle, WA (DLM)
Correspondence to: Karla Kerlikowske, MD, General Internal Medicine Section, San Francisco Veterans Affairs Medical Center, 111A1, 4150 Clement St, San Francisco, CA 94121 (e-mail: karla.kerlikowske{at}ucsf.edu).
In our recent response (1) to correspondences about our report on declines in invasive breast cancer in a screening mammography population, we outlined potential mechanisms that may contribute to a decline in breast cancer, including a decrease in postmenopausal hormone therapy (HT) use, a decline in screening mammography use, an increase in chemoprevention, the increased detection of ductal carcinoma in situ and saturation of mammography screening.
Vaidya suggests an alternative explanation for the decline in invasive breast cancer that we observed in our study, such as lifestyle changes. It is possible that an unmeasured confounder, such as increases in physical activity, could explain some of the decline we observed in invasive breast cancer. However, a large prevalence of women would need to increase their physical activity to influence breast cancer rates because the reduction in breast cancer risk among women who exercise regularly is modest (2).
Vaidya also suggests that an increase in the sensitivity of mammography among former HT users could have influenced breast cancer rates in our population. However, such an explanation is unlikely, given that previous studies have reported mammographic breast density increases in only about 16%–20% of HT users (3,4) and that missed cancers increased from 0.8 to only 1.7 per 1000 screening examinations among long-term HT users (5). As a result, we would expect a very small increase in detection of breast cancers that were formerly obscured by high mammographic breast density associated with HT use.
Vaidya presents data from Scotland showing a precipitous decline in HT use (similar to observations in the United States) without a comparable decline in breast cancer incidence in woman older than 50 years routinely undergoing screening mammography. It is possible that no decline in breast cancer incidence was observed in Scotland because the decline in estrogen and progesterone use occurred predominantly among women who had used estrogen and progesterone for less than 5 years and so were not at increased risk of breast cancer and/or because most formulations of estrogen–progestagen included progesterone or dydrogesterone, hormones that are less likely to increase breast cancer risk (6).
Caan et al. suggest that declines in mammography use among former postmenopausal HT users may have contributed to recent declines in breast cancer incidence in Kaiser women aged 45 years and older. Their figure 1 shows comparable absolute declines in mammography use of about 10% from 2002 to 2003 in women who used HT before 2002 and stopped and in women who continued use after 2002, with both declines starting after the beginning of a decline in breast cancer incidence. Notably, women who were regular HT users before 2002 and who stopped or continued use account for only 6.5% and 5.6%, respectively, of the Kaiser population. Thus, it is unlikely that a small absolute, short-term decline in mammography use among a small population of former and continuous HT users would contribute greatly to a 10% annual decline in breast cancer incidence. Caan et al. show stable to increasing mammography rates among never users of HT (59% of Kaiser women), which explains the minimal change in their overall mammography rates. Because declines in mammography use would need to be large to greatly contribute to a decline in breast cancer incidence, we would not expect the stable overall mammography rates presented by Caan et al. to account for the decline they observed in breast cancer incidence.
REFERENCES
1. Kerlikowske K, Buist DSM, Walker R. Declines in invasive breast cancer and use of postmenopausal hormone therapy in a screening mammography population [reply]. J Natl Cancer Inst (2007) 99(23):1816–1817.
2. Monninkhof EM, Elias SG, Vlems FA, et al. Task Force Physical Activity and Cancer. Physical activity and breast cancer: a systematic review. Epidemiology (2007) 18(1):137–157.[CrossRef][Web of Science][Medline]
3. Greendale GA, Reboussin BA, Sie A, et al. Effects of estrogen and estrogen-progestin on mammographic parenchymal density. Ann Intern Med (1999) 130(4):262–269.
4. Greendale G, Reboussin B, Slone S, Wasilauskas C, Pike MC, Ursin G. Postmenopausal hormone therapy and change in mammographic density. J Natl Cancer Inst (2003) 95(1):30–37.
5. Kerlikowske K, Miglioretti D, Ballard-Barbash R, et al. Prognostic characteristics of breast cancer among postmenopausal hormone users in a screened population. J Clin Oncol (2003) 21(23):4314–4321.
6. Fournier A, Berrino F, Clavel-Chapelon F. Unequal risks for breast cancer associated with different hormone replacement therapies: results from the E3N cohort study. Breast Cancer Res Treat (2008) 107(1):103–111.[CrossRef][Web of Science][Medline]
Related Correspondence
CiteULike 
Connotea 
Del.icio.us What's this?
J Natl Cancer Inst 2008 100: 597-598.
J Natl Cancer Inst 2008 100: 598-599.
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||