An underactive thyroid gland -- a condition afflicting as many as 20 percent of older women -- also apparently lessens a woman's chances of developing an aggressive form of breast cancer, according to a study that provides new evidence for a long-debated link.
Doctors at the University of Texas M.D. Anderson Cancer Center found that women who were diagnosed with hypothyroidism were less likely to have breast cancer, and those who did were likely to have a less-aggressive form of the disease.
The study spotlights the role that hormones besides estrogen play in development and progression of the hormone-sensitive cancer, said Dr. Massimo Cristofanilli, an associate professor of breast oncology and the lead author of the study. The results could help researchers develop new medications for treatment and prevention of breast cancer, he said.
"We have been focusing only on one hormone acting on the breast tissue, but there is a variety of other hormones that create the environment for the development of cancer," Cristofanilli said. "Thyroid appears to be one of them."
Scientists long have been intrigued by the role of the thyroid gland in breast disease. More than a century ago, a doctor in Scotland fed thyroid hormone to women whose breast cancer had spread throughout their body.
Since then, smaller studies on women with several thyroid conditions have generated conflicting results.
The thyroid is a butterfly-shaped gland in the front of the neck that produces a variety of hormones regulating body metabolism. Thyroid hormones affect growth, fertility and the body's use of nutrients and oxygen.
Hypothyroidism occurs when production of these vital hormones slows down. Symptoms can include dry skin, weight gain, sensitivity to cold, forgetfulness and fertility problems. The cause is unknown, although some evidence points to an immune system malfunction, Cristofanilli noted.
The study was published in the online journal Cancer, a publication of the American Cancer Society.
Scientists compared 1,036 women who had been treated for breast cancer to 1,088 healthy women who had attended the hospital's screening clinics.
Women with underactive thyroid glands had a 61 percent lower risk of having invasive breast cancer, or aggressive cancer that had spread into surrounding breast tissue or lymph nodes. Cristofanilli noted that the women with underactive thyroid glands were all taking thyroid hormone replacements, which suggests it is not the thyroid hormone level itself that influences the growth of breast cancer. He said doctors need to study whether the immune system response in these women is playing some role in slowing or preventing breast cancer.
"This is good news, because it indicates that the condition that brings out hypothyroidism is protective enough that it either delays or creates the possibility of developing a less aggressive form of the disease," he said.
Source: Daily Breeze. Powered by Yellowbrix.
