Analysis of overall survival in differentiated thyroid cancer patients with double primary malignancy

Differentiated thyroid cancer (DTC) survivors are at increased risk of developing double primary malignancy (DPM). The aim of this study was to investigate clinicopathological characteristics and survival in DTC patients diagnosed with DPM. A total of 975 patients with DTC diagnosed between 2013 and 2017, treated, and followed at a medical center in Taiwan were retrospectively reviewed. Data from enrolled patients were analyzed for differences in prognosis dependent on the presence of DPM, and which clinicopathological variables affected their prognosis. Among 975 thyroid cancer patients, 94 (9.6%) were diagnosed with DPMs and 16 (1.6%) patients died of any cause. DPM patients had a greater proportion of males, had a higher mean age, more commonly presented with a thyroid mass incidentally by imaging and cervical lymph node metastases, showed a more advanced thyroid cancer stage, and had a higher proportion of lymph node metastases. Overall survival (OS) was significantly lower in patients diagnosed with DPM. Male gender (hazard ratio [HR] = 4.597), two or more DPMs (HR = 8.071), and shorter time interval between two cancers occurrences (HR = 7.101) were significantly risk factors for DPM-related death. In conclusion, the risk of developing DPM in DTC patients was elevated in older, male patients with an advanced tumor-node-metastasis stage. DPM adversely affected the OS of thyroid cancer patients. Male gender, two or more DPMs, and shorter time interval between occurrences were significant risk factors for OS in DPM patients.