Women who survive breast cancer have an increased risk of going on to develop cancer of the thyroid, particularly within five years of their breast cancer diagnosis, a new study has found.

Until now, studies linking breast and thyroid cancer have been mixed, so US researchers decided to assess this further.

Using a US cancer database, they identified over 704,000 women who had been diagnosed with breast cancer between 1973 and 2011, almost 50,000 who had been diagnosed with thyroid cancer and over 1,500 who had been diagnosed with both types of cancer.

The study found that women who had survived breast cancer were at an increased risk of later developing thyroid cancer.

It also found that women who developed thyroid cancer after breast cancer tended to be younger at the time of their breast cancer diagnosis compared to women who only developed breast cancer.

They were also more likely to have developed the most common type of breast cancer and to have received radiation therapy as part of their breast cancer treatment.

Meanwhile, the study also noted that because thyroid cancer usually occurs at a younger age than breast cancer, those who developed thyroid cancer after breast cancer tended to be older than people who only developed thyroid cancer - 62 years versus 45 years.

The researchers emphasised that women who developed thyroid cancer after breast cancer tended to do so within five years. As a result, they recommended that breast cancer survivors should undergo a thyroid check-up every year for the first five years after their breast cancer diagnosis.

"Recognition of this association between breast and thyroid cancer should prompt vigilant screening for thyroid cancer among breast cancer survivors," said the study's lead investigator, Dr Jennifer Hong Kuo, of Columbia University in New York.

Details of these findings were presented at the Endocrine Society's 97th annual meeting in San Diego.