Thyroid Malignant Neoplasia
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Thyroid malignant neoplasia is an autologous growth of thyroid nodules with potential for metastases. There are several types:
- Papillary thyroid carcinoma (PTC)
- Most common variety, 60–70% of thyroid tumors
- Peak incidence in the 3rd to 4th decades
- 3 times more common in women
- May be associated with radiation exposure
- Metastasizes by lymphatic route (30% at time of diagnosis)
- Multicentric in ≥20%, especially in children
- Higher risk in patients with Hashimoto thyroiditis
- Evidence for overdetection “overdiagnosis” of PTC includes increased numbers of smaller size tumors and improved or unchanged survival.
- Many different histologic variants have been described for the thyroid PTC.
- Thyroid tumors currently diagnosed as noninvasive encapsulated follicular variant of papillary thyroid carcinoma (EFVPTC) have a very low risk of adverse outcome and should be termed “noninvasive follicular thyroid neoplasms with papillary-like nuclear features” (NIFTP). This reclassification will affect a large population of patients worldwide and result in a significant reduction in psychological and clinical consequences associated with the diagnosis of cancer.
- Follicular carcinoma
- 10–20% of thyroid tumors
- Peak incidence in 5th decade of life
- Incidence has been decreasing because of the addition of dietary iodine.
- Metastasizes by the hematogenous route
- Hürthle cell carcinoma (variant of follicular with poorer prognosis)
- 2–3% of thyroid malignancies
- Usually in patients >60 years old
- No gender difference
- Variant of follicular carcinoma with worse prognosis
- Medullary thyroid carcinoma (MCT)
- Arises from parafollicular cells, C cells
- Multiple endocrine neoplasia (MEN) syndromes (MEN2A, MEN2B, FMTC). Prevalence of MEN2 is 1:30,000.
- MCT associated with MEN2B occur in childhood, those with MEN2A occur in young adults, and those with FMTC occur at middle age.
- 3–4% of all thyroid tumors
- 25–35% are associated with MEN syndromes (2A more common than 2B), which can be familial or sporadic.
- Calcitonin is a chemical marker.
- RET proto-oncogene mutation is screened; family members who carry the RET gene should consider early prophylactic thyroidectomy.
- Anaplastic carcinoma
- 3% of thyroid tumors
- Most aggressive form of thyroid neoplasia
- More common in females
- Usually in patients >60 years old
- Other: lymphoma, sarcoma, or metastatic (renal, breast, or lung)
- System(s) affected: endocrine/metabolic
- Synonym(s): follicular carcinoma of the thyroid; papillary carcinoma of the thyroid; Hürthle cell carcinoma of the thyroid; anaplastic cell carcinoma of the thyroid
Risk of malignancy increases at >60 years old.
- >60% of thyroid nodules are malignant.
- <2% of thyroid malignancies occur in children and adolescents.
- Increasing tumor size, extrathyroidal extension, and multifocal disease are independent factors associated with nodal metastases in pediatric differentiated thyroid cancer which require careful preoperative evaluation for evidence of lateral cervical lymph node metastases and intraoperative evaluation of the central compartment, with consideration of central lymphadenectomy (1).
- 12.9/100,000 per year in the United States
- Deaths: 0.5/100,000 per year in the United States
- In 2015, estimated 62,450 new cases and 1,950 deaths from thyroid cancer in the United States
- Predominant age: usually >40 years old
- Predominant sex: female > male (2.6:1) prevalence
- Lifetime risk of developing thyroid cancer is 1.1%.
- In 2011, 566,708 patients living with thyroid cancer in the United States
Etiology and PathophysiologyGenetics
- Familial polyposis of the colon, Turcot syndrome, and Gardner syndrome with the APC gene (5q21)
- Medullary: autosomal dominant with MEN syndrome
- BRAF mutation (rare in children)
- RET oncogene (more common in children)
- Family history
- Neck irradiation (6 to 2,000 rads): papillary carcinoma
- Iodine deficiency: follicular carcinoma
- MEN2: medullary carcinoma; autosomal dominant
- Previous history of subtotal thyroidectomy for malignancy: anaplastic carcinoma
- Asian race
- Female gender
- Physical exam in high-risk group
- Calcium infusion or pentagastrin-stimulated calcitonin test screening in high-risk MEN patients
- Screen for RET proto-oncogene in groups at-risk for MCT.
Commonly Associated Conditions
Medullary carcinoma: pheochromocytoma, hyperparathyroidism, ganglioneuroma of the GI tract, neuromata of mucosal membranes