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Hormone Replacement Therapy Possibly Linked to Breast Cancer

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Review on November 26, 2009

For years, researchers have known that prolonged use of hormone replacement therapy during menopause is linked to a greater risk for breast cancer. They also knew that those who develop breast cancer after hormone replacement therapy during menopause are less likely to die from the disease than women who have not had hormone replacement therapy during menopause. The 1999 study by Dr. Melody A. Cobleigh et al., "Hormone Replacement Therapy and High S Phase in Breast Cancer" attempts to explore why this is so. It tackles the problem by studying the different characteristics of the breast cancer that women in each group developed.

The study was conducted between December 1989 and November 1996 from a teaching hospital located in the Midwestern metropolitan area. A total of 331 postmenopausal women were studied, who over the course of time, developed a total of 349 cases of breast cancers. Variables incorporated pathologic tumor size, number of involved nodes last recorded menstrual period, incidence of gynecologic surgery, use of hormone replacement therapy during menopause, type of hormone replacement therapy during menopause and percentage of cells in S phase.

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For the purposes of this study, menopause was referred to hysterectomy, not having a period for one year or being a subject older than 55 years old. Hormone replacement therapy was referred to as receiving estrogen or progestin. There were several categories of women who had taken hormone replacement therapy during menopause: those who had taken hormone replacement therapy up until one month of their diagnosis of breast cancer, those who had stopped hormone replacement therapy before one month of their diagnosis of breast cancer and those who taken hormone replacement therapy (the drug tamoxifen) while undergoing their breast cancer treatment. The biggest group (47%) was women who had never taken hormone replacement therapy during menopause, followed by those presently using hormone replacement therapy (41%), former users of hormone replacement therapy during menopause while only 4 women (1%) took the hormone replacement therapy drug known as tamoxifen.

The S phase (low vs. high) was contrasted between women who had received hormone replacement therapy during menopause and women who had not received hormone replacement therapy during menopause.

The results were that high S-phase cancers had a markedly higher rate of occurrence among women who had received hormone replacement therapy during menopause compared to those who had not received hormone replacement therapy during menopause. However, hormone replacement therapy was found to stimulate growth only in ER-positive cancers. It had little effect on ER negative cancers. The significance of high S-phases in relation to cancer is unknown. It is hypothesized that use of hormone replacement therapy may hasten the growth of cancers in their earlier stages, which is why they are easier to treat once they are caught.

Sources:
  • MD Cobleigh, Melody A.; DO Norlock, Frances E. ; MPH PhD Oleske, Denise M.; Starr, Alexander. "Hormone Replacement Therapy and High S Phase in Breast Cancer"JAMA. 1999.