Breast cancer survivors may be at risk of thyroid cancer

7 Mar 2015

Breast cancer survivors are at increased risk of developing thyroid cancer, especially within five years of their breast cancer diagnosis, according to a new analysis of a large database.

The researchers used the National Cancer Institute's database and they found 704,402 patients with only breast cancer, 49,663 patients with only thyroid cancer and 1,526 patients who developed thyroid cancer after breast cancer.

Results of the comparative study

Compared with patients with breast cancer alone, the researchers found that:

  • Women who had breast cancer followed by thyroid cancer were younger on average when diagnosed with their breast cancer.
  • They also were more likely to have had invasive ductal carcinoma (the most common type of breast cancer), a smaller focus of cancer, and to have received radiation therapy as part of their breast cancer treatment.
  • There was no difference in risk based on whether the breast cancer was hormone receptor positive or had spread to lymph nodes, according to the investigators.

Compared with patients who had only thyroid cancer, it was showed that:

  • Breast cancer survivors who developed thyroid cancer were more likely to have a more aggressive type of thyroid cancer, but the cancers were smaller in size and fewer patients required additional radioactive iodine treatment.
  • Because thyroid cancer tends to occur at younger ages than breast cancer does, breast cancer survivors who then developed thyroid cancer were older on average than those with only thyroid cancer: 62 versus 45 years, respectively.

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The importance of a dedicated thyroid exam

The study findings showed that breast cancer survivors developed thyroid cancer at a median of five years. Therefore, lead investigator Jennifer Hong Kuo, MD, assistant professor of surgery at Columbia University, New York City. recommended that every year for the first five years after a breast cancer diagnosis, especially survivors who received radiation therapy should undergo a dedicated thyroid exam.

"Recognition of this association between breast and thyroid cancer should prompt vigilant screening for thyroid cancer among breast cancer survivors," said Dr. Kuo.

Breast cancer survivor should receive counseling regarding their higher-than-average risk of thyroid cancer, Kuo recommended.

Are breast cancer treatments linked to the increase in thyroid cancer patients?

Until now, Dr. Kuo said, the relationship between breast and thyroid cancer has been controversial, largely based on single-institution studies that have suggested a possible increase in thyroid cancer incidence after breast cancer.

Dr. Kuo said she plans to study whether tamoxifen treatment, typically given for five years after a breast cancer diagnosis, may play a role in increasing the risk of thyroid cancer.

Radiation therapy to the head, neck or chest is a known risk factor for thyroid cancer, according to the Endocrine Society's Hormone Health Network. Female sex raises the risk of both thyroid and breast cancer. The incidence of thyroid cancer is increasing, and Dr. Kuo said researchers must have a better understanding of the etiology for this increase.

Source: Science Daily

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