Purpose: The incidence of the second primary cancer after treatment with radioactive iodine (RAI) is a concern for patients and clinicians. Our objective was to examine the changes that have occurred over a 20-year period in a single institution, by comparing the lifetime observed incidence of the second primary cancer vs those patients with the incidence after the treatment with RAI.
Method: We reviewed all thyroid cancer cases (n = 51) between 1991 and 2010 in the VA New Jersey cancer registry. Patients were distributed into 4 groups consisting of 5-year intervals. These groups were based on accession year and then segregated again into groups that received radioactive iodine and groups that did not. Then, we reviewed the incidence of multiple primaries during the life of the patient and the incidence of a second primary after the diagnoses of thyroid cancer. The incidence of second primary malignancy and age distribution of these groups over the study period was also compared.
Results: An increase in the number of cases diagnosed over the last 20 years was noted. There were a total of 12 cases in the first 10 years compared with 39 cases in the last 10 years. During this period, the total number of all cancer cases accessioned by the registry per year remained stable and constant. However, the increases were significant in the last 5 years; comprising more than half of all cases diagnosed in this 20-year period. There was an observed difference in the average age at diagnosis with the mean age for the first 10 years being 56 years in comparison to the past 10 years, which was 61 years. Also, patients who received radioactive iodine were consistently younger than the group who did not receive RAI. The lifetime incidence of multiple primaries was about 50% in the entire group. The incidence remains similar in each period examined and in all the groups. However, there is an observed difference in the incidence of second primary in the RAI group after treatment compared with those who did not received RAI.
Conclusions: There was an increase in the incidence of thyroid cancer diagnosed over the 20-year period, and the overall incidence of multiple primaries during this time span remained consistent. However, the observed incidence of the second primary after the diagnoses of thyroid cancer was higher in the group who received RAI treatment.