Thyroid Cancer

Intro & Risks - Gland Gone Wild

• Most common endocrine malignancy; incidence ↑, especially in women.
• Major Types:
  • Papillary (MC, 80-85%), Follicular (10-15%), Medullary (~3-5%), Anaplastic (<2%, worst prognosis).
  • 📌 Poor Fat Mice Always (Papillary, Follicular, Medullary, Anaplastic).
• Key Risk Factors:
  • Radiation exposure: Childhood/adolescent head & neck (e.g., for lymphoma). Dose-dependent.
  • Family Hx/Genetic Syndromes:
    • Medullary: MEN2A/2B (RET proto-oncogene), Familial Medullary Thyroid Cancer (FMTC).
    • Papillary: Familial Adenomatous Polyposis (FAP), Gardner syndrome, Cowden syndrome (PTEN gene).
  • Iodine deficiency: ↑ risk for Follicular cancer.
  • Chronic TSH stimulation (e.g., Hashimoto's thyroiditis - controversial for papillary; established link to thyroid lymphoma).

⭐ Thyroid cancer is the most common endocrine malignancy. Papillary thyroid cancer (PTC) is its most prevalent subtype, often with an excellent prognosis if detected early and managed appropriately.

Classification & Path - Rogues' Gallery

• Papillary Carcinoma (PTC): ~80-85%.
  • Path: Orphan Annie eye nuclei (intranuclear inclusions, grooves), psammoma bodies.
  • Spread: Lymphatic. Prognosis: Excellent.
  • Variants: Follicular, Tall cell (worse prognosis).

  ⭐ Papillary thyroid cancer: most common type, psammoma bodies, excellent prognosis.

• Follicular Carcinoma (FTC): ~10-15%.
  • Path: Capsular/vascular invasion essential for diagnosis (FNAC cannot diagnose).
  • Spread: Hematogenous (bone, lung). 📌 "Follicular Follows Vessels."
  • Hürthle cell variant: more aggressive.
• Medullary Carcinoma (MTC): ~3-5%.
  • Origin: Parafollicular C-cells. Secretes calcitonin.
  • Path: Amyloid stroma (Congo red positive).
  • Associations: MEN 2A/2B (RET mutation).
• Anaplastic Carcinoma (ATC): <1-2%.
  • Undifferentiated, highly aggressive. Often elderly.
  • Prognosis: Dismal, rapidly fatal.
• Lymphoma: Rare. Often arises in Hashimoto's thyroiditis.

Diagnosis & Staging - Detective Work

• Clinical Evaluation: Neck swelling, hoarseness, dysphagia. Family Hx (Medullary Ca).
• Thyroid Function Tests (TFTs): Usually euthyroid. TSH (suppressed in hot nodule, ↑ in Hashimoto's).
• Ultrasound (USG) Neck: Initial imaging. High-risk features: solid, hypoechoic, microcalcifications, irregular margins, taller-than-wide, extrathyroidal extension, suspicious lymph nodes.
• Fine Needle Aspiration Cytology (FNAC):

  ⭐ Fine Needle Aspiration Cytology (FNAC) is the gold standard investigation for a thyroid nodule.

  • Bethesda System for Reporting Thyroid Cytopathology (BSRTC) guides management.
• Staging (AJCC 8th Ed): TNM. Age is key for Differentiated Thyroid Cancer (DTC).
  • Papillary/Follicular: Age <55 yrs (Stage I/II). Age ≥55 yrs (Stage I-IV).
  • Medullary: Calcitonin/CEA levels for prognosis & follow-up.
  • Anaplastic: All Stage IV (universally poor prognosis).

Management & Follow-up - Battle Plan

• Primary Treatment
  • Surgery: Total Thyroidectomy (TT) ± Central/Lateral Neck Dissection. Lobectomy for select low-risk (e.g., unifocal papillary microcarcinoma $<$1cm, no ETE/mets).
• Adjuvant Therapy (Risk-Stratified)
  • Radioactive Iodine (RAI; I-131): Post-TT for remnant ablation/adjuvant. Dose: 30-150 mCi.
  • TSH Suppression: Levothyroxine. Goal: TSH $<$0.1 mU/L (high-risk), 0.1-0.5 mU/L (low/intermediate-risk).

  ⭐ TSH suppression therapy is crucial post-thyroidectomy for differentiated thyroid cancer (DTC) to reduce recurrence.

• Advanced/Recurrent Disease
  • EBRT: Unresectable, mets (bone, brain).
  • TKIs (Lenvatinib, Sorafenib): RAI-refractory DTC.
• Follow-up (Dynamic Risk Assessment)
  • Serum Tg, Anti-TgAb, TSH (q 6-12 months).
  • Neck Ultrasound (q 6-12 months).
  • Further imaging (CT, MRI, PET) as indicated.

High‑Yield Points - ⚡ Biggest Takeaways

• Papillary Thyroid Carcinoma (PTC): Most common, excellent prognosis, psammoma bodies, lymphatic spread.
• Follicular Carcinoma: Hematogenous spread (bone, lungs); FNAC cannot diagnose invasion (histology needed).
• Medullary Carcinoma: From C-cells, produces calcitonin, linked to MEN2 (RET oncogene), amyloid stroma.
• Anaplastic Carcinoma: Elderly patients, worst prognosis, rapidly aggressive and often fatal.
• FNAC is the best initial diagnostic test for evaluating suspicious thyroid nodules.
• Differentiated cancers (PTC, Follicular): Treat with total thyroidectomy, radioiodine ablation, TSH suppression.