Clinical behavior and genetics of nonsyndromic, familial nonmedullary thyroid cancer

Nonmedullary thyroid cancer (NMTC) is one of the most inheritable forms of all cancers with an 8- to 10-fold risk of a first-degree relative developing disease. Familial nonmedullary thyroid cancer (FNMTC) describes this familial aggregation and is comprised of two distinct subgroups; syndromic and nonsyndromic. Greater than 85% of thyroid tumors in nonsyndromic FNMTC are papillary thyroid cancer, followed by FTC (∼10%), poorly differentiated, and anaplastic thyroid cancer (∼5%). Compared to sporadic NMTC, FNMTC presents at a younger age and is associated with a higher incidence of multifocal disease and metastasis. The transmission pattern most frequently follows an autosomal dominant mode of inheritance. While there has been extensive investigation to find a high-penetrant, single locus as the causative genetic factor, more recent data suggest that FNMTC is a polygenic disorder with variable penetrance likely associated with a low-to-moderate number of low-penetrant alleles. A number of case-controlled, familial and population-based studies using genomewide association single-nucleotide polymorphism arrays have begun to unravel the complex genetic environment of FNMTC. These studies highlight the significant challenges in identifying markers predictive of disease onset and progression. Continued efforts will hopefully lead to identification of a panel of genetic markers used to identify family members at risk. Until this time, clinical factors appear to be the most efficient and accurate method for surveillance and diagnosis.