Second Primary Malignancy Risk in Thyroid Cancer Survivors: A Systematic Review and Meta-Analysis

OBJECTIVE: To determine the risk of second primary malignancies (SPMs) in thyroid cancer survivors. DESIGN: We performed a systematic review and meta-analysis examining the standardized incidence ratios (SIRs) of SPMs in thyroid cancer survivors (compared to individuals without thyroid cancer). Two independent reviewers screened citations and reviewed all full-text papers deemed potentially relevant. Final consensus was reached on inclusion of papers in the review. Data were pooled using fixed effects models. MAIN OUTCOMES: Thirteen full-text papers were included. The incidence of SPMs in thyroid cancer survivors was increased with an SIR of 1.20 (95% confidence interval 1.17, 1.24) (based on pooled data from six studies of 70,844 thyroid cancer survivors). The SIR of the following SPMs was significantly increased: salivary gland, stomach, colon/colorectal, breast, prostate, kidney, brain/central nervous system, soft tissue sarcoma, non-Hodgkin's lymphoma, multiple myeloma, leukemia, bone/joints, and adrenal. A significantly reduced risk of lung and cervical cancers was observed. CONCLUSIONS: Thyroid cancer survivors are at increased risk of SPMs, which may be related to disease-specific treatments or genetic predisposition.