Quantitative Pharmacology-Based Dose Adjustment Protocol in Postoperative Thyroid Cancer Patients

Inclusion criteria

• Aged 18-65 years, inclusive, regardless of sex.
• Able to fully understand the study and voluntarily sign the informed consent form.
• Histologically or cytologically confirmed advanced or metastatic thyroid cancer, treatment-naïve, and requiring total or near-total thyroidectomy.
• Eastern Cooperative Oncology Group (ECOG) performance status ≤2.
• No clinically significant contraindications to surgery.
• Body weight ≥50.0 kg for males and ≥45.0 kg for females, with a body mass index (BMI) of 19.0-26.0 kg/m², inclusive.
• Able to maintain regular daily routines, communicate effectively with the investigator, comply with all study requirements, and adhere to scheduled study visits, treatment plans, and laboratory assessments.
• Adequate baseline organ function at the screening visit, as demonstrated by local laboratory values meeting the protocol-specified eligibility requirements.

Exclusion criteria

• Thyroid cancer patients for whom the planned or completed thyroidectomy does not meet the criteria for total or near-total thyroidectomy.
• Prior treatment for thyroid cancer, including surgery and/or pharmacological treatment.
• Major surgery, including radiosurgery, or significant traumatic injury within 2 weeks prior to randomization.
• History of another malignancy within 3 years prior to initiation of study treatment.
• Known history of a positive human immunodeficiency virus (HIV) test.
• Known active hepatitis B virus (HBV) or hepatitis C virus (HCV) infection; chronic or resolved HBV or HCV infection is permitted.
• Congenital or acquired immunodeficiency.
• History of clinically significant drug allergy or atopic allergic disease (e.g., asthma, urticaria, or eczematous dermatitis), or known hypersensitivity to Euthyrox (levothyroxine sodium) or any of its excipients.
• Pregnant or breastfeeding females.