Risk of second primary lung cancer in patients with thyroid cancer: a meta-analysis based on big population studies

BACKGROUND: Previous studies have revealed that the number of cancer survivors developing a second primary malignancy is increasing, especially among thyroid cancer patients, and lung cancer is still the main cause of cancer death. Therefore, we aimed to investigate the risk of second primary lung cancer (SPLC) in patients with thyroid cancer. METHODS: We searched the PubMed, Web of Science, Embase, and Scopus databases up to November 24, 2021, for relevant research and merged the standardized incidence ratios (SIRs) and 95% confidence intervals (95% CIs) to evaluate the risk of developing SPLC in patients with thyroid cancer. RESULTS: Fourteen studies involving 1,480,816 cases were included in our meta-analysis. The pooled result demonstrated that thyroid cancer patients may have a higher risk of SPLC than the general population (SIR = 1.21, 95% CI: 1.07–1.36, P < 0.01, I(2) = 81%, P < 0.01). Subgroup analysis stratified by sex indicated that female patients may have a markedly higher risk of SPLC than male patients (SIR = 1.65, 95% CI: 1.40–1.94, P < 0.01, I(2) = 75%, P < 0.01). CONCLUSIONS: Thyroid cancer patients are more likely to develop SPLC than the general population, especially women. However, other risk factors must be investigated, and more prospective studies are needed to confirm our results. REGISTRATION: International Prospective Register of Systematic Reviews: No. CRD42021285399.