The diagnostic process for thyroid cancer usually begins when a nodule is detected in the thyroid gland. The primary and most crucial examination method is thyroid ultrasonography. If a thyroid nodule with suspicious characteristics for cancer is identified during ultrasonography, a fine needle aspiration biopsy (FNAB) is performed. FNAB, considered the gold standard worldwide for the preliminary diagnosis of thyroid cancer, is evaluated by a cytologist. If the biopsy results suggest malignancy, the definitive diagnosis is typically established through a detailed examination of surgically removed thyroid tissue by a pathologist.

Additionally, the following methods may be used in the diagnostic process:
* Blood Tests: Thyroid hormone levels and specific cancer markers (e.g., calcitonin) can be evaluated.
* Imaging Methods (CT, MRI): Computed tomography (CT) and magnetic resonance imaging (MRI) may be utilized to assess cancer spread or distant metastases.