Swedish study ties HRT to raised risk of breast ca: estrogen-only replacement therapy was not linked to increased breast cancer risk. (Combined Continuous HRT).

SAN ANTONIO -- Progestin-containing hormone replacement therapy was associated with a markedly increased breast cancer risk, but estrogen-only replacement therapy was not, according to the findings of a huge Swedish study

Indeed, the yearly risk of breast cancer in a woman who has used progestin-containing hormone replacement therapy (HRT) for at least 4 years is roughly equivalent to half that associated with carrying a BRCAI mutation, Dr. Hakan Olsson reported during a breast cancer symposium sponsored by the San Antonio Cancer Institute.

An important observation was that the overall risk of cancer in the Swedish study was not increased in HRT users.

"The increased risk of breast and endometrial cancers in the cohort is balanced by a reduced risk for some other tumor types, especially colon cancer and smoking-related cancers. What we're doing with HRT is shifting the tumor sites around," said Dr. Olsson, professor of medicine at the University of Lund, Sweden.

He reported on nearly 30,000 Swedish women aged 25-65 with no history of cancer who enrolled in a prospective cohort study during 1990-1992. This study population, which constitutes one in eight women in this age group living in southern Sweden, now has roughly 227,000 person-years of follow-up.

To date, 585 breast cancers have been detected in participants. Among women with naturally occurring menopause, the risk of breast cancer climbed with increasing duration of HRT use such that those with more than 48 months of use had an 80% greater risk than never-users after controlling for conventional breast cancer risk factors, including patient age, family history, parity age at first term pregnancy, and age at menarche and at menopause.

The increased risk conferred by HRT use disappeared, however, after 5 years off the therapy.