Survival Outcomes Associated with Hypothyroidism Following Cancer Therapies

BACKGROUND: Hypothyroidism is a recognized adverse effect of cancer therapies such as immune checkpoint inhibitors (ICI), tyrosine kinase inhibitors (TKI), and radiotherapy. Although proposed as an indicator of treatment response, its prognostic significance across cancer types and therapies remains underexplored. This study evaluated survival outcomes associated with treatment-induced hypothyroidism. METHODS: We conducted a retrospective cohort study using de-identified electronic health record data from the University of Michigan (2006-2023). Adults (≥18 years) receiving ICIs, TKIs, or radiotherapy, without prior thyroid disease or malignancy, were included. We defined hypothyroidism by institutional laboratory criteria or thyroid hormone initiation. Time-dependent Cox models estimated hazard ratios (HRs) and 95% confidence intervals for overall and cancer-specific survival, adjusting for demographic, clinical, and lifestyle factors. Analyses were stratified by treatment class and cancer sites; sensitivity analyses assessed robustness. RESULTS: = 0.021). Results were consistent across sensitivity analyses. CONCLUSIONS: Hypothyroidism after ICI and radiotherapy was associated with improved survival, supporting its potential as a prognostic biomarker of therapeutic benefit. Future studies should investigate the underlying mechanisms and clinical implications.