SAT-378 - Pregnancy Occurring after Thyroid Cancer Diagnosis Is Associated with Superior Survival: A Multi-State Linked Registry Analysis

Background:
Differentiated thyroid cancer (DTC) is common among women of reproductive age, yet the impact of pregnancy on survival remains unclear. Prior studies report conflicting outcomes for women diagnosed with DTC during pregnancy or who conceive after treatment. Few population-based analyses have evaluated whether pregnancy influences overall (OS) or disease-specific survival (DSS). This study examined the association between pregnancy after DTC diagnosis and survival outcomes.

Methods:
We linked birth records and cancers diagnosed during 1989–2018 from seven states participating in the Surveillance Epidemiology and End Results Program. Our analytic cohort included women aged 20-49 years with DTC. Pregnancies were classified as occurring at or after DTC diagnosis. Demographic, tumor, treatment, and mortality data were provided from cancer registry records; birth records supplied pregnancy-related variables. Our primary outcome was OS; secondary outcome was DSS. Kaplan-Meier curves and log-rank tests compared groups, and Cox models estimated adjusted hazard ratios (HR) while adjusting for demographic, clinical, and reproductive factors. Missing data were managed using complete case analysis or multiple imputation.

Results:
A total of 17,769 women were included, of whom 3,058 (20.7%) became pregnant at or after DTC diagnosis. Median age at diagnosis was 37 years, with median 11.6 years of follow-up. There were 575 deaths, including 77 DTC–specific deaths. OS was significantly higher among women who became pregnant (log-rank p < 0.001), with 10- and 20-year survival of 99.5% and 98.0% vs. 97.0% and 93.0% in non-pregnant women. In Cox models, pregnancy remained associated with improved OS (HR 0.54, 95% CI 0.37–0.79, p = 0.001) after adjusting for age, stage, tumor size, additional malignancies, race/ethnicity, year of diagnosis, and pregnancy-related factors. DSS was also significantly higher among women who became pregnant after DTC diagnosis (log-rank p < 0.001); however, in multivariable analysis, this association was no longer statistically significant. Stage-stratified analyses suggested that pregnancy confers an OS benefit among women with distant metastases at diagnosis (log-rank p = 0.03), though few events limited multivariable modeling.

Conclusion:
Pregnancy occurring post-DTC diagnosis is associated with higher OS, reflecting either a physiologic phenomenon or residual confounding from health status and other unmeasured factors. These findings provide population based evidence to support counseling that pregnancy is generally safe for women with DTC and does not appear to negatively influence long term survival. More detailed data on comorbidities, progression, and preclinical modeling of pregnancy-induced effects on tumor biology are needed to further clarify these associations.

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