Abstract
Background
Mutually increased risks for thyroid and breast cancer have been reported, but the contribution of etiologic factors versus increased medical surveillance to these associations is unknown.
Methods
Leveraging large-scale US population-based cancer registry data, we used standardized incidence ratios (SIRs) to investigate the reciprocal risks of thyroid and breast cancers among adult females diagnosed with a first primary invasive, non-metastatic breast cancer (N = 652,627) or papillary thyroid cancer (PTC) (N = 92,318) during 2000–2017 who survived ≥1-year.
Results
PTC risk was increased 1.3-fold [N = 1434; SIR = 1.32; 95 % confidence interval (CI) = 1.25–1.39] after breast cancer compared to the general population. PTC risk declined significantly with time since breast cancer (Poisson regression = P trend <0.001) and was evident only for tumors ≤2 cm in size. The SIRs for PTC were higher after hormone-receptor (HR)+ (versus HR-) and stage II or III (versus stage 0-I) breast tumors. Breast cancer risk was increased 1.2-fold (N = 2038; SIR = 1.21; CI = 1.16–1.26) after PTC and was constant over time since PTC but was only increased for stage 0-II and HR + breast cancers.
Conclusion
Although some of the patterns by latency, stage and size are consistent with heightened surveillance contributing to the breast-thyroid association, we cannot exclude a role of shared etiology or treatment effects.
1
Introduction
A number of studies have reported increased risk for thyroid cancer among breast cancer survivors and the reciprocal increased risk for breast cancer among thyroid cancer survivors [ , ]. Past studies have hypothesized that the association between breast and thyroid cancers may be explained by shared etiological factors (e.g., genetic factors [ PTEN -mutation] and obesity) or treatment received for initial cancer [ ]. Additionally, cancer survivors undergo heightened clinical surveillance, which may result in incidental detection of primarily early-stage, small-sized tumors that may not have become clinically apparent during the patient’s lifetime [ , ]. While it is established that this more intensive clinical surveillance immediately after diagnosis can result in spuriously inflated risks of subsequent malignancies compared with the general population [ ], prolonged heightened surveillance also has been suggested as a potential explanation for the observed increased risks of these second breast and thyroid cancers [ , , ]. However, previous studies have not systematically assessed breast and thyroid cancer risks by latency, stage, and tumor size.
Reviews
There are no reviews yet.