Deciphering the Risk of Developing Second Primary Thyroid Cancer Following a Primary Malignancy—Who Is at the Greatest Risk?

SIMPLE SUMMARY: Associations between thyroid cancer and breast cancer have been elucidated, in that patients with breast cancer have a greater risk of developing subsequent thyroid cancer. However, not much is known about the relationship other primary cancers and subsequent thyroid cancer. In this review, we completed a thorough review of the existing literature to understand the relationship between primary cancers and second primary thyroid cancer (SPTC). Our findings suggest that surveillance protocols should be considered for patients at a higher risk of SPTC, including those with primary breast, renal cell, basal cell, and ovarian cancers who are female and/or Caucasian. ABSTRACT: Background: It is critical to understand factors that may contribute to an increased risk of SPTC in order to develop surveillance protocols in high-risk individuals. This systematic review and meta-analysis will assess the association between primary malignancy and SPTC. Methods: A search of PubMed and Embase databases was completed in April 2020. Inclusion criteria included studies that reported the incidence or standardized incidence ratio of any primary malignancy and SPTC, published between 1980–2020. The PRISMA guidelines were followed and the Newcastle–Ottawa Scale was used to assess quality of studies. Results: 40 studies were included, which were comprised of 1,613,945 patients and 15 distinct types of primary cancers. In addition, 4196 (0.26%) patients developed SPTC following a mean duration of 8.07 ± 4.39 years. Greater risk of developing SPTC was found following primary breast (56.6%, 95%CI, 44.3–68.9, p < 0.001), renal cell (12.2%, 95%CI, 7.68–16.8, p < 0.001), basal cell (7.79%, 95%CI, 1.79–13.7, p = 0.011), and ovarian cancer (11.4%, 95%CI, 3.4–19.5, p = 0.005). SPTC patients were more likely to be females (RR = 1.58, 95%CI, 1.2–2.01, p < 0.001) and Caucasians (p < 0.001). Conclusions: Surveillance protocols should be considered for patients at a higher risk of SPTC, including those with primary breast, renal cell, basal cell and ovarian cancers who are female and/or Caucasian.