Nonthyroidal second primary malignancies in differentiated thyroid cancer patients: Is the incidence increased comparing to the general population and could it be a radioiodine therapy consequence?

다국어 초록 (Multilingual Abstract)

The long‐term survival of differentiated thyroid cancer (DTC) patients and the need to perform several treatments with radioiodine (131‐I) lead to the question if the lifetime risk of developing a nonthyroidal second primary cancer (NTSPC) is increased in these patients. In our study, we assessed the prevalence of NTSPCs in thyroid cancer population and evaluated the possible causative role of 131‐I treatment. We analyzed 1096 consecutive patients followed at our institution from 1964 to 1998. A total of 101 NTSPCs were observed in 92/1096 patients (8.4%) among which 17/101 (16.8%) diagnosed before DTC and 84/101 (83.2%) diagnosed after. The most frequent tumor sites observed were breast and bladder/urinary tract in the post‐DTC group and breast and hematological system in the pre‐DTC group. Regarding 131‐I treatment, we did not observe any significant differences regarding either the number of treatments or the cumulative activity. The only significant parameter associated with an increased incidence of NTSPC was follow‐up (P = .02): a longer follow‐up period was associated with a higher number of NTSPCs. The mean latency between 131‐I and NTSPC was 10.52 ± 7.69 years. Comparing with the general Italian population, independent of radioiodine treatment, the standard incidence ratio in our cohort was similar to that of the general population (SIR 1.07) and this result was confirmed by analyzing only the treated group. In conclusion, these results show that the risk of NTSPCs in the DTC patients' population is similar to that in the general population and 131‐I treatment was not associated with an increased risk.
What's new?
Whether radioiodine treatment for differentiated thyroid cancer (DTC) increases risk of second non‐thyroidal primary cancer (NTSPC) is unclear. In this retrospective study, second primary cancer incidence was investigated in more than 1000 DTC patients treated with radioiodine in Italy from 1964 to 1998. Analyses show that 8.4% of patients had NTSPCs, though about one‐sixth of these were diagnosed before DTC. Despite the frequency of NTSPC, independent of radioiodine, overall NTSPC risk in patients was not significantly different from risk in the general Italian population. Moreover, radioiodine treatment was not correlated with increased cumulative risk of second primary cancer.