The goal of this study is to find out whether hypothyroidism caused by immune checkpoint inhibitors (ICIs) can recover after stopping the ICIs. The study also aims to identify factors that can help predict which patients will be able to stop taking thyroid hormone replacement.

The main questions the study will answer are:

• What percentage of patients recover normal thyroid function and can stop levothyroxine after stopping ICIs?
• What clinical or laboratory factors can predict successful withdrawal of levothyroxine?

Participants will:

• Be adult cancer patients who developed hypothyroidism during ICI treatment and are currently taking levothyroxine
• Have already stopped ICI therapy
• Gradually reduce their levothyroxine dose every 3 months if their thyroid function remains normal
• Stop levothyroxine if thyroid function remains normal at low doses (≤0.025 mg)
• Be monitored with thyroid function tests and clinical symptoms at each visit

Inclusion Criteria:

• Adults aged 19 years or older.
• Patients with a history of treatment with immune checkpoint inhibitors (ICIs).
• Developed hypothyroidism during ICI treatment and initiated levothyroxine after starting ICI therapy.
• Discontinued ICI therapy prior to study enrollment.

Exclusion Criteria:

• Use of levothyroxine or antithyroid medications within 3 months prior to initiating ICI therapy.
• History of thyroid surgery, radioactive iodine therapy, or neck radiation therapy.
• Current levothyroxine dose ≥0.1 mg at the time of enrollment.