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Swedish Study Finds Increased Risk of Breast Cancer With Progestin-Containing HRT

Swedish Study Finds Increased Risk of Breast Cancer With Progestin-Containing HRT

SAN ANTONIO—A large Swedish cohort study of hormone replacement therapy (HRT)
use and breast cancer suggests that women on progestin-containing regimens are
three times more likely to develop breast cancer than are women who have never
used HRT. Estrogen-only preparations, in contrast, did not appreciably increase
the risk, said Hakan Olsson, MD, professor of oncology, University Hospital,
Lund, at the 25th Annual San Antonio Breast Cancer Symposium (abstract 34).

The cohort consisted of 30,000 women age 25 to 65 who were first interviewed
through a structured questionnaire between 1990 and 1992. The women were all
Swedish born, with no evidence of any type of cancer at the time. The
questionnaire addressed health issues such as hormonal and reproductive
factors, family history, constitutional factors, alcohol and smoking history,
and sun exposure.

Recall of hormone exposure was facilitated through use of color charts of
the name and time period when various types of hormone preparations had been
used. Dr. Olsson said his group has almost complete follow-up of the cohort,
which now constitutes 298,649 person-years.

At the 2001 follow-up, 556 breast cancers had been diagnosed, compared with
an expected 508. The peak exposure to HRT in the cohort occurred at age 54, at
which time about 30% of the women had used hormone replacement, Dr. Olsson
said. He noted that overall risk of cancer (all types) was not increased,
indicating that the increased risk of breast and endometrial cancers was being
balanced by a decreased risk of some other types of cancer, such as colon
cancer and smoking-related cancers.

The researchers reported their initial results in 2001 (Br J Cancer
85:674-677, 2001). "In our first results, overall HRT use gave an 80% increased
risk of breast cancer after 4 years of use," Dr. Olsson said. "This risk was
independent of other risk factors, and it disappeared after the woman had
stopped HRT for 5 years."

He noted that there was no synergy between HRT use and family history of
breast cancer—both were independent risk factors. Moreover, previous users of
oral contraceptives did not have a higher risk of breast cancer when they took
HRT.

In their second study, the researchers analyzed breast cancer risk by type
of HRT. Dr. Olsson noted that several previous studies of the issue had found a
higher risk among women who had taken a combination of estrogen and progestin
than among those who had taken estrogen alone. However, the studies were not
consistent in determining whether the type of combined therapy—combined
continuous therapy or combined sequential therapy—made a difference. His group
attempted to address this issue by looking at all types of HRT.

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