Thyroid

Epidemiology
About 30,000 cases per year in the US; 1500 deaths
Incidence is increasing, possibly related to an increase in imaging studies leading to incidental finding of thyroid lesion

Risk factors
Well established relationship to radiation exposure especially in childhood
Histology is usually papillary adenocarcinoma
HLA-DR7 is associated with non-radiation associated papillary thyroid cancer

Lymph node drainage
Pretracheal and delphian nodes in addition to II, III, IV

Pathology
1) Papillary
Most common subtype (papillary is popular)
Associated with radiation exposure
Excellent prognosis
Two to four times more common in women
Tall cell, insular subtypes cary a worse prognosis
Propensity for lymph node spread

2) Follicular
Strongest affinity for I-131
Also more common in women (2-3x)
Associated with hematogenous mets (lymph node mets are rare)
Hurthle cell, clear cell are variants

3) Medullary
Parafollicular/C cells
Does not concentrate I-131 but can be treated with I-131 anyway due to uptake in the rest of the thyroid gland
Associated with MEN-II

4) Anaplastic
Highly aggressive
Associated with transformed goiter

5) Radiation-induced
Similar histologic distribution as sporadic cases
Tumors may have a greater tendency to invade and recur
Treated the same as other thyroid cancers

Treatment
All patients: surgery, exogenous thyroid hormone (to suppress stimulation of the thyroid gland)
I-131 ablation if tumor is greater than 1cm, has capsular invasion, vascular invasion, positive margins, positive nodes, recurrent disease
External radiation if tumor does not concentrate I-131; multiply recurrent; bulky/unresectable disease