A study looked at the health histories of more than 30,000 women and men from 2 months to almost 30 years after they were treated for thyroid cancer. The researchers found that people diagnosed with thyroid cancer had a slightly higher risk of developing a second cancer within the first 10 years after their thyroid cancer treatment. After these first 10 years, risk WASN'T higher for a second cancer.
A second cancer is a new, different type of cancer, not the previously treated thyroid cancer coming back. Several different types of second cancers were seen, including breast cancer in women and prostate cancer in men.
Women between 25 to 49 years old who were previously treated for thyroid cancer had a small but definite increase in their risk for breast cancer. Because of this, the researchers recommended that younger women diagnosed with thyroid cancer start having annual mammograms within 3 years after diagnosis.
Researchers aren't sure why thyroid cancer treatment seems to increase the risk of a second cancer. Radioactive iodine is a common treatment for both an overactive thyroid gland and thyroid cancer. This treatment is considered safe and effective, but it's possible that radioactive iodine could trigger cancer in a very small number of people. Other research has shown that cancer risk, including breast cancer risk, is higher after radioactive iodine is used to treat an overactive thyroid gland. It's also possible that the genetic or other factors that contributed to a person developing thyroid cancer might increase risk for other types of cancer.
If you've been treated for any type of cancer in the past, make sure your doctor understands your unique medical history and is aware of any risks related to your past treatments. Your doctor can give you the counseling, monitoring, and screening you need to manage those increased risks. Your plan might include a more aggressive approach to breast cancer screening, including starting annual mammograms at an earlier age and other imaging techniques, such as MRI.