Affiliation of authors: C. Magnusson, I. Persson, Department of Medical Epidemiology, Karolinska Institutet, Stockholm, Sweden; H.-O. Adami, Department of Medical Epidemiology, Karolinska Institutet, and Department of Epidemiology and Harvard Center for Cancer Prevention, Harvard University, Boston, MA.
Correspondence to: Cecilia Magnusson, M.D., Ph.D., Department of Medical Epidemiology, Karolinska Institutet, P.O. Box 281, 171 77 Stockholm, Sweden (e-mail: Cecilia.Magnusson{at}mep.ki.se).
The influence of combined estrogenprogestin replacement therapy on breast cancer risk is important in the riskbenefit equation associated with hormone replacement therapy. Thus, the lack of data on this relationship is of considerable concern to the millions of treated women. Therefore, it was with great interest we read the report in the Journal by Ross et al. (1). Last year, we published results from a casecontrol study conducted in Sweden (2), where combined estrogenprogestin therapy has been the predominant therapy for many years. We thought it might be of interest to make a comparison between the only two studies where the influence of sequential estrogen plus progestin replacement therapy (SEPRT) and continuous combined estrogen plus progestin replacement therapy (CCRT) has been explored. The Swedish study included 3345 case patients and 3454 control subjects, with response rates of 84% and 82%, respectively (2). We reported that risk of breast cancer increased with duration of use of both SEPRT and CCRT, yet, in contrast to the findings of Ross et al. (see Table 1), the relative risk (RR) associated with SEPRT was substantially lower (RR = 1.03 per year of use; 95% confidence interval [CI] = 0.941.13) than the corresponding risk associated with CCRT (RR = 1.19 per year of use; 95% CI = 1.091.31). These estimates were statistically significantly different from one another (P for heterogeneity = .03).
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We believe that neither our study (2) nor the study by Ross et al. (1) provides the full picture regarding the possibly different effects of SPRT and CCRT on breast cancer risk but only that a comparison between the two is interesting. Indeed, this important question needs further investigation.
NOTES
Editor's note: Ronald K. Ross et al. declined to respond to the correspondence of Cecilia Magnusson et al.
REFERENCES
1
Ross RK, Paganini-Hill A, Wan PC, Pike MC. Effect of hormone replacement therapy on breast cancer risk: estrogen versus estrogen plus progestin. J Natl Cancer Inst 2000;92:32832.
2 Magnusson C, Baron JA, Correia N, Bergstrom R, Adami HO, Persson I. Breast-cancer risk following long-term oestrogen- and oestrogen-progestin replacement therapy. Int J Cancer 1999;81:33944.[Medline]
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