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INTRODUCTION

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Thyroid malignancies are classified on the basis of the origin of cells into medullary thyroid cancer (MTC), which originates from the parafollicular cells, and nonmedullary thyroid cancer (NMTC), which originates from the follicular cells. NMTC mainly includes papillary and follicular thyroid cancer (PTC and FTC). Both PTC and FTC are differentiated thyroid cancers that constitute the vast majority of thyroid cancers (>90%) and carry an excellent prognosis with an overall 5-year survival exceeding 95%. 1-4

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Both MTC and NMTC can occur sporadically or as part of an inherited syndrome or familial predisposition. This chapter will focus on the diagnosis and management of nonsyndromic familial NMTC (FNMTC) and NMTC associated with inherited syndromes (Table 50-1). Inherited syndromes involving MTC such as multiple endocrine neoplasia type 2 (MEN2a, familial MTC and MEN2b) are not covered in this chapter.

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TABLE 50-1:

The Clinical Features Associated with Familial Thyroid Cancer Syndromes

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NONSYNDROMIC FAMILIAL NONMEDULLARY THYROID CANCER

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Familial NMTC is commonly defined by the presence of well-differentiated thyroid cancer (WDTC) in two or more first-degree relatives in the absence of predisposing hereditary syndromes (i.e., Cowden syndrome, Gardner's syndrome) or environmental factors (ionizing radiation to the neck, iodine deficiency). 5,6 It is estimated that FNMTC accounts for 3% to 10% of all the thyroid cancer cases with an autosomal dominant pattern of inheritance with incomplete penetrance. 6-9 However, the true incidence of FNMTC is not known, and it is estimated that PTC is in fact sporadic in 45% to 69% of the cases with only two affected family members. 10

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The most common histologic subtype of FNMTC is PTC. Women seem to be affected approximately two to three times more than men and the age at diagnosis for patients with FNMTC seems to be less than that of sporadic cases (41 vs. 47). 6,8,10-12 This, however, may be an artifact of early screening for patients with ...

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