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(Drug information on 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.
