Multiple primary tumors in differentiated thyroid carcinoma and relationship to thyroid cancer outcome

Patients with differentiated thyroid carcinoma (DTC) have long-life expectancy and are at risk for developing a second primary cancer. Aim of this study was to assess the occurrence of DTC in conjunction with other primary neoplasms. It was also aimed to explore the possibility of synchronous or metachronous other malignancies having an impact on clinical course of thyroid carcinoma.

Clinical records of 1680 DTC patients treated and followed in our institution over last twenty years were reviewed. Forty-five second primary tumors were found in 42 patients. These patients were classified into 3 groups as antecedent (group I), synchronous (group II) or subsequent (group III) according to the timing of occurrence of non-thyroidal malignancy. The initial characteristics of thyroid neoplasm were compared between patients with DTC plus another tumor and DTC only. Kaplan-Meier Survival Analysis was used to estimate the survival probability for patients with DTC alone and DTC plus another primary tumor.

There were 15 synchronous and 30 metachronous tumors in 42 patients. Three of them had triple tumors. The most common second primary was lympho-haematological and upper aero digestive system tumors in group I and II respectively, whereas a variety of tumors were noted in group III. Despite the more common occurrence of unfavourable prognostic factors in patients with multiple cancers than thyroid cancer alone, complete response to radioiodine therapy and recurrence free survival rate was similar in both groups (p>0.05).

The results of the current series imply that the occurrence of multiple primary tumors is not uncommon in patients with DTC. Close medical surveillance and the use of advanced screening modalities might lead to the detection of second primary tumors in DTC. However, the presence of second primary seems not to affect the clinical course of DTC.