Increased risk of certain second primary malignancies in patients treated for well-differentiated thyroid cancer

Background

The objective was to evaluate the incidence of second primary malignancies (SPMs) in thyroid cancer patients compared to age- and gender-matched controls without thyroid cancer from the general population of the same region.

Methods

Tampere and Oulu University Hospitals treated 910 patients with well-differentiated thyroid cancer during 1981–2002. The Finnish cancer registry provided follow-up data for patients and controls (n = 4542) for an average of 16 years. The incidence of invasive malignancies per 10 000 person-years was calculated and compared between patients and controls. The follow-up period ended December 31st, 2011.

Results

Young patients <40 years [Rate Ratio (RR) 1.73, p = 0.037] and patients diagnosed since 1996 (RR 1.51, p = 0.029) had an increased incidence of SPMs. Patients had an increased risk of sarcomas and soft tissue tumours (RR 4.37, p = 0.004) and haematological and lymphatic malignancies (RR 1.87, p = 0.035), especially non-Hodgkin lymphomas (RR 2.78, p = 0.035). The overall incidence of SPMs was not statistically higher in patients (109 SPMs/910 patients vs. 500 SPMs/4542 controls, RR 1.12, p = 0.269). Most patients were radioiodine-treated (81 %). The risk of SPMs with low cumulative radioiodine doses was RR 0.94 (≤3.7 GBq, p = 0.650) and with high doses RR 1.37 (>3.7 GBq, p = 0.143). Cumulative radioiodine dose increased during the study period.

Conclusions

The overall incidence of SPMs was not higher in patients than in controls. The incidence of SPMs in thyroid carcinoma patients was higher in patients <40 years old and patients diagnosed since 1996. The incidence of sarcomas and lymphomas was higher in patients than in controls.