Impact of second primary malignancy on outcomes of differentiated thyroid carcinoma

There are few data on the degree to which thyroid cancer survivors are at risk of second primary malignancy (SPM). This study aimed at evaluating the risk of SPM in patients with differentiated thyroid carcinoma (DTC) and how the timing of SPM might affect the disease course.

Among 1,043 patients diagnosed with DTC between 1970 and 2008, 27 (2.6%) had synchronous SPM (ie, diagnosed within 6 months of DTC) and 71 (6.8%) had metachronous SPM (ie, diagnosed > 6 months after DTC) in 10,419 person-years of follow-up. Standardized incidence ratios were estimated overall and for each SPM site.

DTC survivors had a 39% greater risk of SPM (SIR = 1.39; 95% CI, 1.09-1.73) compared to the general population. Those with SPM had a worse overall survival than those without SPM (P < .001). The synchronous group had a worse DTC-specific survival (P = .002), whereas the metachronous group had a worse SPM-specific survival (P = .042). A lesser proportion in the metachronous group were able to receive curative treatment for SPM (32/71 vs 20/27; P = .013).

DTC survivors had an increased risk of SPM. The occurrence of SPM adversely affected the survival of DTC. The synchronous group tended to die from DTC, whereas the metachronous group from SPM. Heightened postoperative surveillance might improve survival.