Reproductive, hormonal factors influence risk of thyroid cancer

NEW YORK (Reuters Health) – Certain reproductive patterns–and a history of postpartum thyroiditis in particular–are risk factors for thyroid cancer in women, according to a report in the January 1st issue of the International Journal of Cancer.

To investigate the association between reproductive and hormonal factors and thyroid cancer, Dr. Anjum Memon, of Kuwait University, Safat, and colleagues conducted a population-based, case-control interview study of 238 women diagnosed with thyroid cancer and matched controls in Kuwait, where "thyroid cancer is the second most common neoplasm among women."

The average age at diagnosis was 34.7 years, the team notes. Women with at least 12 years of education had a significantly reduced risk of thyroid cancer (odds ratio [OR] = 0.4; p < 0.05). They observed no relationship between age at menarche, pregnancy, menopausal status, and age at menopause and thyroid cancer.

There was a significantly increased risk of thyroid cancer among women who had their last pregnancy at age 30 years or older (OR = 2.1). "There was also a significant trend in risk with increasing age at last pregnancy," the investigators note. They observed a modest increase in risk among women with at least five births (OR = 1.5).

"A substantial recent-birth effect, in relation to subsequent diagnosis of thyroid cancer, was observed during the second and third year after a birth (OR = 2.0)," Dr. Memon and colleagues report.

Spontaneous abortion appeared to have a protective effect. The researchers report that risk was significantly decreased among women who had a miscarriage as the outcome of first pregnancy (OR = 0.1) and women who had at least three miscarriages (OR = 0.3).

A history of postpartum thyroiditis was associated with a significantly increased risk (OR = 10.2). "The possible link between this condition and thyroid cancer has not been studied before," the authors point out. They acknowledge that the finding could be due to differential recall, but they say the strength of the association is consistent with previous findings showing a connection between other benign thyroid conditions and subsequent cancer.

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