A study recently published in the journal “Cancer” has discovered that therapy with the drug tamoxifen — an oral medication used in women with breast cancer — is linked to a significant increase in development of diabetes in older survivors of breast cancer.
The study was headed by Lorraine L. Lipscombe, M.D., with the Women’s College Hospital in Toronto. Dr. Lipscombe’s team studied 14,360 women over the age of 65 who had been diagnosed with early-stage breast cancer and had survived. The women had received treatment for breast cancer with tamoxifen therapy. The study used data collected from 1996 to 2006; the patients who were diagnosed with diabetes through March 31, 2008 were matched with control subjects who had not developed diabetes. The research team adjusted for other risk factors and compared the risk of developing diabetes in participants who received tamoxifen and aromatase inhibitor therapy compared to women who were not treated with those drugs.
According to the study’s findings, 10 percent of the patients received a diagnosis of diabetes over a mean follow-up of 5.2 years. Women who were currently receiving tamoxifen therapy had a significantly higher chance of developing diabetes (1.24 adjusted odds ratio) over women who were not being treated with tamoxifen. Treatment with aromatase inhibitors, on the other hand, was found not to be linked to an increased risk of developing diabetes.
“Current tamoxifen therapy is associated with an increased incidence of diabetes in older breast cancer survivors. These findings suggest that tamoxifen treatment may exacerbate an underlying risk of diabetes in susceptible women,” wrote the authors of the study.
Tamoxifen, marketedd as Nolvadex, Istubal, and Valodex in the U.S., is an orally-administered tablet that disrupts the female body’s production of estrogen, which is known to promote breast cancer in women. Tamoxifen binds to the estrogen receptor proteins, effectively blocking additional binding at the site that would cause cancerous growth. Tamoxifen is approved by the FDA for the treatment of breast cancer and other types of cancer and has been used for over 30 years in the treatment of early-stage breast cancer.
The drug has also been used to reduce the risk of breast cancer in women who are at increased risk of developing the disease. It works by blocking the effects of estrogen on breast cancer cells with estrogen receptor-positive proteins, preventing the growth of the cancerous cells. However, the medication is only useful in treating cancer cells that are specifically estrogen receptor-positive. Doctors must determine whether the tumor will respond to tamoxifen treatment before prescribing the drug.
Tamoxifen therapy is known to be associated with several serious side effects, including stroke, blood clots, uterine cancer, and cataracts. It may also cause symptoms similar to menopause such as hot flashes, irregular menstrual periods, headaches, nausea, and fatigue. Though tamoxifen therapy does cause blood clots or stroke in a small number of women, the chances of developing such complications are similar to those associated with estrogen replacement therapy.
Additional adverse side effects associated with tamoxifen therapy include an increased risk of thromboembolism and fatty liver as well as mental effects such as reduced cognition and degraded memory, though memory loss with tamoxifen therapy is not as severe as with aromatase inhibitor therapy. Tamoxifen has also been associated with reduced libido.
However, not all the side effects of tamoxifen therapy are negative; it is known to improve bone health, especially in women, by inhibiting osteoclasts and preventing osteoporosis.