Postmenopausal Hormone Therapy Increases Breast Cancer Risk Across All Ethnicities

Previous studies have already revealed a link between menopausalhormone therapy and increased breast cancer risk. The relative risk isgreatest for women taking estrogen-progestin therapy. But most studieshave focused on white women, and few considered prognostic factors suchas body mass index, stage of disease, histologic subtype, and hormonereceptor status. Researchers, led by Sulggi Lee of the Keck School ofMedicine at the University of Southern California, Norris ComprehensiveCancer Center decided to examine these factors in relation to theincreased breast cancer risk associated with hormone therapies.

They utilized the Multiethnic Cohort Study which includes215,251 men and women, aged 45 to 75 who were living in Hawaii orCalifornia in 1993. They focused on 55,371 African-American, NativeHawaiian, Japanese American, Latina and White postmenopausal women andgathered health and medical information each woman had provided uponher enrollment into the cohort. They then crosschecked for subsequentincidents of invasive breast cancer using local and state cancerregistries through the end of 2001. There were 1,615 such cases, andfor each, the researchers obtained data on tumor characteristics,cancer stage and receptor status.

The researchers found that current use of estrogen-progestintherapy was associated with an increased breast cancer risk--29 percenthigher after five years of use. The association applied to women in allethnic groups. Current use of estrogen therapy was also associated withincreased risk--10 percent higher after five years of use. Thisassociation was seen in all ethnic groups except for African-Americans.

Interestingly, relative breast cancer risks for current use ofestrogen-progestin therapy was greater for women with low body massindex (BMI below 25), even though clear increases were also seen inwomen with higher BMIs. "Data on this aspect of the relationshipbetween hormone therapy use and risk is scarce and it is too early todraw a firm conclusion," the authors report.

The effect of current estrogen-progestin therapy use onlocalized disease was greater than on advanced disease, in agreementwith most previous studies. And hormone therapy was associated withincreased risk of both ductal and lobular carcinomas.Estrogen-progestin therapy was significantly associated with ER+/PR+tumors, but non-significantly associated with increases in ER+/PR- andER-/PR+ tumors. Estrogen therapy was associated with both ER+/PR+ andER+/PR- tumors--all consistent with the findings of earlier studies.

In interpreting results of this study, "it is important toconsider certain methodological issues," say the authors. It ispossible that patients were lost to follow-up, though the out-migrationfrom California and Hawaii is very low. It's also possible that resultswere biased upward because users of hormone therapy are screened morefrequently for breast cancer; however, adjustment of the results forthe frequency of mammograms reported by the women at baseline had verylittle effect on these results. Lastly, the true duration of hormonetherapy is unknown, since use was only assessed at baseline; however,the results quoted above are minimum estimates of risk as they werebased on assuming that women using hormones at baseline continued to doso.

In conclusion, report the authors, "this study provides someof the first results comparing breast cancer risk among differentracial/ethnic groups in relation to hormone therapy use. The resultssuggest that risk among women of other races is similar to the riskpreviously reported among whites."

Article: "Postmenopausal Hormone Therapy and Breast Cancer Risk: TheMultiethnic Cohort," Sulggi Lee, Laurence Kolonel, Lynne Wilkens, PeggyWan, Brian Henderson, and Malcolm Pike. International Journal ofCancer; Published Online: September 16, 2005 (DOI: 10.1002/ijc.21481);Article is available via Wiley InterScience (www.interscience.wiley.com/journal/ijc) upon online publication.