A new study indicates that women with abnormally low thyroid function - a condition known as hypothyroidism - seem to be protected to some degree against breast cancer.

“The results of this retrospective study indicated that women with hypothyroidism have a reduced risk of developing breast cancer,” Dr. Massimo Cristofanilli of the M. D. Anderson Cancer Center, Houston, told AMN Health.

And if these women are diagnosed with breast cancer, the tumor seems to be of a less aggressive type.

Cristofanilli and his colleagues note in the medical journal Cancer that the possible link between thyroid disease and breast cancer “has been debated for decades and remains controversial.”

To shed more light on the matter, the team studied 1136 women with primary breast carcinoma who were matched to 1088 healthy women who had attended a breast screening clinic.

In total, 242 (about 11%) of the women in the study had hypothyroidism. However, the rate of hypothyroidism was 15% among the comparison group without breast cancer, significantly higher than the 7% rate among women with breast cancer.

Also, among the breast cancer patients, those who did have hypothyroidism were older at the time of cancer diagnosis and the disease was less advanced than in women with normal thyroid function, the team found

“These data strongly suggest a role of thyroid hormone in breast carcinogenesis, possibly in close relationship with estrogen,” Cristofanilli said.

SOURCE: Cancer, March 15, 2005.