56. Thyroid cancer

• For initial evaluation, follow the diagnostic approach to thyroid nodules.

  • TSH, ultrasound, potentially scintigraphy

  • Confirmation: fine-needle aspiration cytology (FNAC) or intraoperative frozen-section

• Thyroid tumor markers help to estimate the prognosis and assess response to therapy.

  • Differentiated thyroid cancer: serum thyroglobulin (Tg)

  • Medullary carcinoma: serum calcitonin and carcinoembryonic antigen (CEA)

• Staging of lymph node and distant metastases

Serum TSH and ultrasound should be obtained in all patients with thyroid nodules.

• TSH: typically normal or mildly elevated [14]

• Thyroid ultrasound: to assess for sonographic signs of thyroid malignancy [11][14]

  • Solid or mostly solid hypoechoic nodule(s)

  • Irregular margins

  • Microcalcifications within nodules

  • Nodules that are taller than wide

  • Extrathyroidal growth

• Indications

  • Thyroid nodule(s) with ↓ TSH levels

  • Multinodular thyroids (to identify nodules that require FNAC)

• Contraindications: pregnant and breastfeeding women

• Supportive findings: decreased or no radiotracer uptake (i.e., hypofunctioning or nonfunctioning nodules, referred to as cold nodules

• Fine-needle aspiration cytology (FNAC)

  • Indications: sonographic signs of thyroid cancer detected on thyroid ultrasound (see “Indications for FNAC of thyroid nodules”)

  • Supportive findings: typically reported as “malignant” or “suspicious for malignancy” according to the Bethesda system for thyroid cytopathology

If cytology is nondiagnostic or of undetermined significance, consider repeating FNAC under ultrasound guidance or consider molecular testing or lobectomy and frozen-section to assess for thyroid cancer.

Thyroid cancer tumor markers

The specific tumor markers depend on the histological type of the cancer.

• Follicular or papillary thyroid cancer

  • Thyroglobulin (Tg): precursor of thyroid hormones; produced exclusively by the thyroid gland [14]

    • Indicated after total thyroidectomy or RAIA therapy

    • Baseline (pretreatment) levels are not routinely indicated.

• Medullary carcinoma

  • Calcitonin: A hormone secreted by parafollicular cells, which is the tissue of origin of medullary carcinoma

    • Indicated preoperatively if FNAC is suspicious for medullary carcinoma (supportive diagnostic marker) [8][11])

    • Used to monitor response to therapy

  • Carcinoembryonic antigen (CEA): nonspecific marker, used in combination with calcitonin to monitor response to therapy[8]