Radioactive Iodine for Thyroid Cancer Lowers Birthrate in Women

Pam Harrison

January 27, 2015

Women in their 30s who receive radioactive iodine (RAI) for the treatment of well-differentiated thyroid cancer have around a 30% lower birthrate than their peers with the same disease who did not have RAI, new research, published in the January issue of Thyroid, shows.

"One really simple explanation for these findings is that after they receive RAI, patients are instructed not to have children for a number of months, and for women who are between 35 and 39 years of age, that waiting period may cause some of them to be pushed out of that short interval where they might remain fertile," lead author Dr James Wu (University of California, Los Angeles, David Geffen School of Medicine) told Medscape Medical News.

"So I think this paper reinforces the importance of having the endocrinologist initiate a conversion with a woman in this age range who still desires childbirth. If they are 35 and really want to have a child, and they are at low risk even without receiving RAI, then maybe they might just defer having it," he suggested.

Study Details

Dr Wu and colleagues retrospectively studied 25,333 patients with well-differentiated thyroid cancer, 18,850 of whom were women, enrolled in the California Cancer Registry (CCR).

The CCR is a prospectively maintained, statewide cancer database containing unique patient identifiers that permits longitudinal follow-up.

Of the women with well-differentiated thyroid cancer, 52.4% received RAI ablation after their initial surgery.

The women were followed for a median of 4 years, during which 1179 live births occurred after 6 months following the diagnosis of thyroid cancer.

"RAI ablation did not affect birthrate among women in the full data set," Dr. Wu and colleagues report.

However, among those between the ages of 35 and 39 years, the birthrate — at 11.5 per 1000 patient-years — was significantly lower among those who received RAI than among those who did not, at 16.3 births per 1000 patient-years (P < .001).

Importantly as well, the median time to first live birth following the diagnosis of well-differentiated thyroid cancer was significantly prolonged at 34.5 months among women who received RAI, compared with 26.1 months for those who did not (P < .0001).

Median Time to First Delivery (mo) Following Initial Presentation

Age Category Received RAI Did Not Receive RAI
20–29 39.3 28.0
25–29 34.7 27.8
30–34 30.8 23.7
35–39 30.6 24.2
Difference in all age categories, P < .05

When stratified by tumor size and stage, RAI ablation was still associated with a significant delay in median time to first live birth after adjustment for confounding variables among patients with both localized and regional disease, the authors add.

Ubiquitous Use of RAI Should Engender Discussion With Older Women

As Dr Wu explained, after RAI was shown to have a positive effect for patients with thyroid cancer, "its use became ubiquitous."

This was despite the fact that the most recent guidelines from the American Thyroid Association (from 2009) suggested that patients with low-risk thyroid cancer — who represent the majority of patients with well-differentiated thyroid cancer — do not need RAI.

"We looked at this and said, if we can come at this issue using a large registry with many thousands of patients, maybe we can find a small but significant adverse effect of RAI if you are at low risk," Dr Wu explained.

"I don't think that this study is strong enough to suggest that older women between the ages of 35 and 39 should not receive RAI, because we just don't have that causal link," he added.

"But it's a good enough reason to initiate a discussion about the pros and cons of RAI with older women, and at the same time, it's reassuring for women under the age of 35 to know that while they may end up waiting longer to have a child if they receive RAI, in the end their overall fertility is unaffected."

Dr Wu reports no relevant financial relationships. Disclosures for the coauthors are listed in the article.

Thyroid. 2015;25:133-138. Abstract

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