Second malignancies in patients with differentiated thyroid carcinoma treated with low and medium activities of radioactive I-131

BACKGROUND AND AIM This study aimed at determining whether there is a risk regarding the development of second primary malignancies after patient exposure to the low and medium radioiodine activity used during the treatment of differentiated thyroid cancers (DTC). METHODS Second primary malignancies that occurred after DTC were detected in 1,990 patients treated between 1970 and 2003. The mean long-term follow-up period was 182 months. RESULTS Radioiodine I-131was administrated at a mean dose of 63.2 mCi. There were 93 patients with at least one second primary malignancy. The relative risk of development of second malignancy in DTC patients was increased (p<0.0001) for breast, uterine and ovarian cancers compared with the general population. CONCLUSIONS The overall risk concerning the development of second primary malignancies was related to the presence of DTC, but not to exposure to the low and medium activities of radioiodine administered as adjuvant therapy.