Risk of Second Primary Malignancy in Patients Treated with Radioactive
Iodine for Thyroid Cancer
ABSTRACT Introduction Radioactive iodine (RAI) is widely used as a
treatment for differentiated thyroid cancer following total
thyroidectomy. There is a risk of second primary malignancy (SPM) in
these patients which is estimated between 0-5% although research to
support this is limited. The primary aim of this study was to ascertain
the rate of SPM in patients who have undergone RAIT for thyroid cancer.
The secondary objectives were to assess whether the risk is dose
dependant and examine the overall survival and recurrence rates. Methods
A retrospective review of all patients treated with radioactive iodine
for thyroid cancer between 2002 and 2014. Patient information was
collected from a structured database. Data regarding second cancers and
recurrence rates was obtained from an online clinical portal. Follow up
was 5 years minimum. Results 199 patients underwent RAI treatment.
Median age was 53. 71.4% patients were female and 28.6% were male. All
patients underwent total thyroidectomy. 13.6% underwent total thyroid
and central neck dissection. 11% underwent total thyroidectomy and
lateral neck dissection. 5.5% required post-operative radiotherapy.
12% patients developed recurrent thyroid cancer. 8% developed a SPM of
which prostate, skin, head and neck SCC were the most common. A dose
≥3.7 (Gigabecquerel) GBq was statistically significantly more likely to
lead to a SPM with a P value of 0.041 (95% CI -0.52 – 0.01318).
Conclusions Increased risk of developing a second primary malignancy
should be taken into account, especially in younger patients with low
risk disease, when deciding on RAIT. Key words Radioactive iodine,
Differentiated thyroid cancer, Second primary malignancy, Radioiodine,