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Researchers Find that More Than Three Years of Hormone Replacement Therapy May Increase Risk of Lobular Breast Cancer (dateline January 23, 2008)

Results from the largest study of its kind show that using hormone replacement therapy (HRT) for over three years could increase the risk of a certain type of breast cancer called lobular carcinoma. Earlier research had shown that more than five years of HRT use could increase breast cancer risk. The results of the new study suggest that the risk may occur earlier.

Lobular carcinoma is a type of invasive breast cancer that begins in the begins in the milk glands (lobules) of the breast. However, the cancer often spreads (metastatizes) to other regions of the body. Lobular carcinoma accounts for about 10% to 15% of breast cancers, but the researchers of this latest study say that diagnoses have been on the rise since the late 1980s. Lobular carcinoma tends to be easier to treat than other types of breast cancer because it is hormonally sensitive; however, it can be more difficult to detect than ductal carcinomas.

Hormone replacement therapy (HRT) is synthetic estrogen and progesterone (progestin) designed to "replace" a woman's depleting hormone levels. HRT is used to treat symptoms of menopause, including hot flashes, irregular menstrual periods, and vaginal dryness. These and other menopausal symptoms vary in severity for women. Women who have their uteruses in tact usually take a combined estrogen/progestin form of HRT because estrogen alone can increase the risk of endometrial cancer-cancer of the uterine lining.

Past research has shown that the use of hormone replacement therapy may increase the risk of breast cancer, particularly lobular carcinoma in situ. However, the research generally showed that women who took HRT for more than five years developed the increased breast cancer risk.

To further investigate this issue, Christopher I. Li and his colleagues from the Fred Hutchinson Cancer Research Center in Seattle, Washington analyzed data from 1,500 post-menopausal women. Over 1,000 of the women had been diagnosed with certain types of breast cancer (lobular, mixed ductal-lobular, or ductal) and 469 had not been diagnosed with breast cancer.

The researchers found that women who had taken an estrogen/progestin combination of hormone-replacement therapy had a "substantially increased risk" of developing breast cancer (a 2.7-fold increased risk of lobular carcinoma and a 3.3-fold increased risk of developing ductal-lobular cancer), even after accounting for individual characteristics of the women's cancer such the number of lymph nodes involved.

Although lobular cancer is less common than other types of cancer, such as ductal carcinoma, the researchers say the results of the study are alarming because they show that HRT may increase breast cancer risk earlier than thought. However, further research is needed to confirm the findings. In the meantime, women considering HRT to relieve menopausal symptoms are encouraged to speak to their physicians about the benefits and risks of HRT (including duration of use), given their individual medical situation.

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