Background: Thyroid cancer is commonly diagnosed in the first postpartum year, supporting the theory that high levels of estrogen may stimulate progression of hormone-mediated thyroid cancer. The aim of this study was to assess the effect of recent pregnancy on histopathologic disease characteristics of well-differentiated thyroid cancer (WDTC).
Methods: Cases of WDTC (1999-2012) were identified from the California Cancer Registry and linked to data from the Office of Statewide Health Planning and Development. Using a matched control design, recently pregnant women (pregnancy up to five years before and nine months after a thyroid cancer diagnosis) were compared with non-pregnant controls matched by age and race/ethnicity. The main outcome measures were histopathologic tumor characteristics (tumor size, extrathyroidal extension, and nodal metastases), disease status at last follow-up, and five-year disease-specific survival.
Results: The study sample of 1204 women (Mage ± standard deviation = 30.9 ± 5.5 years; 46.5% Caucasian and 40.0% Hispanic) included 301 recently pregnant women matched against 903 non-pregnant controls. Comparing recently pregnant versus non-pregnant women, no significant differences were observed with respect to tumor size (M = 2.2 ± 1.6 vs. 2.3 ± 3.9 cm; p = 0.39), extrathyroidal extension (12.0% vs. 14.1%; p = 0.46), stage at diagnosis (localized disease: 67.4% vs. 62.8%; regional metastases: 30.6% vs. 33.4%; distant metastases: 2.0% vs. 3.8%; p = 0.17), disease status at last follow-up (free of tumor vs. not free of tumor; p = 0.48), and five-year disease-specific survival (99.5% vs. 99.5%). In multivariate analyses, after controlling for patient age and ethnicity, recent pregnancy was not a significant predictor of tumor size, extrathyroidal extension, nodal metastases, or distant metastases.
Conclusions: In this cohort, recent pregnancy was not associated with high-risk pathological features of differentiated thyroid cancer. These findings provide reassurance with regards to the concern that pregnancy may act as a potential stimulus for thyroid cancer growth.
Keywords: childbearing; postpartum; pregnancy; thyroid cancer; women.