Results of a standardized written interview of 29,508 swedish women indicate that use of hormone replacement therapy (HRT) containing progestins significantly elevates breast carcinoma risk whereas estradiol use does not.

While HRT is becoming more frequently used at and after menopause, the overall long-term health consequences are not fully understood. One possible negative effect is the increased risk for breast carcinoma, particularly after prolonged HRT use. Some studies have suggested an increased risk for preparations containing estrogen and progestins, in contrast to those containing estrogen alone. Furthermore, it is not known whether combined continuous or combined sequential HRT therapy is more strongly associated with breast carcinoma risk. Sequential HRT more closely mimics the natural hormone cycle, which alternates between high estrogen and high progesterone levels.

In the current study, researchers investigated the risk for breast cancer in relation to the type of HRT, exposure time, and reproductive risk factors (i.e. age at menarche, parity, age at first full-term pregnancy, and family history of breast carcinoma). Data was collected from 29,508 Swedish women by standardized written interviews. Results indicate that progestin-containing brands are associated with the highest risk.

After more than 4 years of exposure, risk more than doubled for women taking combined estrogen and progestin HRT, whereas those taking estriol and estradiol showed a lower risk and those taking estradiol alone demonstrated insignificant risk. Researchers found a 7% risk for breast carcinoma in patients after 4 years of combined HRT, compared with a 2% risk among never users. This data also suggests that continuous administration of progestin-containing HRT is the most hazardous.

In light of these findings, women taking HRT may wish to discuss preparation and administration options with their doctor.

Reference: Olsson HL, Ingvar C, Bladstrom A, Hormone replacement therapy containing progestins and given continuously increases breast carcinoma risk in Sweden.

Cancer. 2003; 97: 1387-1392.

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