Risks of breast and endometrial cancer after estrogen and estrogen-progestin replacement.
OBJECTIVE
We studied the risk of breast and endometrial cancer in a cohort of 11,231 Swedish women prescribed different replacement hormone regimens.


METHODS
All 10,472 women at risk of developing breast cancer and 8,438 women at risk of endometrial cancer were followed up from the time of the questionnaire in 1987-88 through 1993, by record-linkages to the National Swedish Cancer Registry. Using data from a questionnaire we analyzed the relationships between hormone exposures and cancer risk, with non-compliers and users of less than 1 year as a reference group.


RESULTS
For breast cancer, women reporting use of estrogens combined with progestins had evidence of an increased risk relative to women denying intake or taking hormones for less than 1 year; relative risk (RR) = 1.4 (95% confidence interval 0.9-2.3) after 1-6 years of intake, and RR = 1.7 (95% CI 1.1-2.6) after more than 6 years. This excess risk seemed confined to recent exposure. We found no association with intake of estrogens alone using non-compliers and short-term takers as the reference group. The risk of invasive endometrial cancer was increased four-fold in women using medium-potency estrogens alone for 6 years or longer, RR = 4.2 (95% CI 2.5-8.4). Women on such long-term progestin-combined treatment had a lower, non-significant, excess risk (RR = 1.4; 95% CI 0.6-3.3).


CONCLUSIONS
We conclude that long-term recent use of estrogen-progestin combined replacement therapy may increase the risk of breast cancer. Exposure to estrogen alone substantially elevates the risk of endometrial cancer, an increase that can be reduced or perhaps avoided by adding progestins.
Persson
I
I
Department of Medical Epidemiology, Karolinska Institutet, Stockholm, Sweden.
Weiderpass
E
E
Bergkvist
L
L
Bergström
R
R
Schairer
C
C
D001943:Breast Neoplasms / Q000139:chemically induced / Q000453:epidemiology*; D015331:Cohort Studies; D016889:Endometrial Neoplasms / Q000139:chemically induced / Q000453:epidemiology*; D004967:Estrogens / Q000009:adverse effects*; D005260:Female; D020249:Hormone Replacement Therapy / Q000009:adverse effects*; D006801:Humans; D008875:Middle Aged; D011372:Progestins / Q000009:adverse effects*; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013548:Sweden / Q000453:epidemiology
D004967:Estrogens; D011372:Progestins