DICER1 tumor predisposition (DICER1) is characterized by an increased risk for pleuropulmonary blastoma (PPB), pulmonary cysts, thyroid gland neoplasia (multinodular goiter, adenomas, and/or thyroid cancer), ovarian tumors (Sertoli-Leydig cell tumor, gynandroblastoma, and sarcoma), and cystic nephroma. Less commonly observed tumors include ciliary body medulloepithelioma, nasal chondromesenchymal hamartoma, embryonal rhabdomyosarcoma, pituitary blastoma, pineoblastoma, central nervous system (CNS) sarcoma, other CNS tumors, and presacral malignant teratoid tumor. The majority of tumors occur in individuals younger than age 40 years. PPB typically presents in infants and children younger than age six years. Ovarian sex cord-stromal tumors are most often diagnosed before age 40 years. Cystic nephroma generally presents in young children but has also been reported in adolescents. Additional clinical features that may be seen include macrocephaly, ocular abnormalities, structural anomalies of the kidney and collecting system, and dental anomalies (bulbous crowns).

Alagille syndrome (ALGS) is a multisystem disorder with a wide spectrum of clinical variability; this variability is seen even among individuals from the same family. The major clinical manifestations of ALGS are bile duct paucity on liver biopsy, cholestasis, congenital cardiac defects (primarily involving the pulmonary arteries), butterfly vertebrae, ophthalmologic abnormalities (most commonly posterior embryotoxon), and characteristic facial features. Renal abnormalities, growth failure, developmental delays, splenomegaly, and vascular abnormalities may also occur.

APC-associated polyposis conditions include (classic or attenuated) familial adenomatous polyposis (FAP) and gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS). FAP is a colorectal cancer (CRC) predisposition syndrome that can manifest in either classic or attenuated form. Classic FAP is characterized by hundreds to thousands of adenomatous colonic polyps, beginning on average at age 16 years (range 7-36 years). For those with the classic form of FAP, 95% of individuals have polyps by age 35 years; CRC is inevitable without colectomy. The mean age of CRC diagnosis in untreated individuals is 39 years (range 34-43 years). The attenuated form is characterized by multiple colonic polyps (average of 30), more proximally located polyps, and a diagnosis of CRC at a later age than in classic FAP. For those with an attenuated form, there is a 70% lifetime risk of CRC and the mean age of diagnosis is 50-55 years. Extracolonic manifestations are variably present and include polyps of the stomach and duodenum, osteomas, dental abnormalities, congenital hypertrophy of the retinal pigment epithelium (CHRPE), benign cutaneous lesions, desmoid tumors, adrenal masses, and other associated cancers. GAPPS is characterized by proximal gastric polyposis, increased risk of gastric adenocarcinoma, and no duodenal or colonic involvement in most individuals reported.

Cowden syndrome is a genetic disorder characterized by multiple noncancerous, tumor-like growths called hamartomas and an increased risk of developing certain cancers.\n\nAlmost everyone with Cowden syndrome develops hamartomas. These growths are most commonly found on the skin and mucous membranes (such as the lining of the mouth and nose), but they can also occur in the intestine and other parts of the body. The growth of hamartomas on the skin and mucous membranes typically becomes apparent by a person's late twenties.\n\nCowden syndrome is associated with an increased risk of developing several types of cancer, particularly cancers of the breast, a gland in the lower neck called the thyroid, and the lining of the uterus (the endometrium). Other cancers that have been identified in people with Cowden syndrome include kidney cancer, colorectal cancer, and an agressive form of skin cancer called melanoma. Compared with the general population, people with Cowden syndrome develop these cancers at younger ages, often beginning in their thirties or forties. People with Cowden syndrome are also more likely to develop more than one cancer during their lifetimes compared to the general population. Other diseases of the breast, thyroid, and endometrium are also common in Cowden syndrome. Additional signs and symptoms can include an enlarged head (macrocephaly) and a rare, noncancerous brain tumor called Lhermitte-Duclos disease. A small percentage of affected individuals have delayed development, intellectual disability, or autism spectrum disorder, which can affect communication and social interaction.\n\nSome people do not meet the strict criteria for a clinical diagnosis of Cowden syndrome, but they have some of the characteristic features of the condition, particularly the cancers. These individuals are often described as having Cowden-like syndrome. Both Cowden syndrome and Cowden-like syndrome are caused by mutations in the same genes.\n\nThe features of Cowden syndrome overlap with those of another disorder called Bannayan-Riley-Ruvalcaba syndrome. People with Bannayan-Riley-Ruvalcaba syndrome also develop hamartomas and other noncancerous tumors.  Some people with Cowden syndrome have relatives diagnosed with Bannayan-Riley-Ruvalcaba syndrome, and other affected individuals have the characteristic features of both conditions. Based on these similarities, researchers have proposed that Cowden syndrome and Bannayan-Riley-Ruvalcaba syndrome represent a spectrum of overlapping features known as PTEN hamartoma tumor syndrome (named for the genetic cause of the conditions) instead of two distinct conditions.\n\n

Nonmedullary thyroid cancer (NMTC) refers to neoplasms originating from the thyroid follicular cells and represents 80 to 95% of all thyroid cancers. Approximately 5% of NMTC occurs on the background of a familial predisposition. Although papillary thyroid carcinoma (PTC) is usually the most frequent thyroid lesion in NMTC families, multinodular goiter (MNG) and follicular thyroid adenoma also occur (summary by Pereira et al., 2015). For a general phenotypic description and a discussion of genetic heterogeneity of NMTC, see NMTC1 (188550).

Nonmedullary thyroid cancer (NMTC) comprises thyroid cancers of follicular cell origin and accounts for more than 95% of all thyroid cancer cases. The remaining cancers originate from parafollicular cells (medullary thyroid cancer, MTC; 155240). NMTC is classified into 4 groups: papillary, follicular, Hurthle cell (607464), and anaplastic. Approximately 5% of NMTC is hereditary, occurring as a minor component of a familial cancer syndrome (e.g., familial adenomatous polyposis, 175100, Carney complex, 160980) or as a primary feature (familial NMTC or FNMTC). Papillary thyroid cancer (PTC) is the most common histologic subtype of FNMTC, accounting for approximately 85% of cases (summary by Vriens et al., 2009). Follicular thyroid cancer (FTC) accounts for approximately 15% of NMTC and is defined by invasive features that result in infiltration of blood vessels and/or full penetration of the tumor capsule, in the absence of the nuclear alterations that characterize papillary carcinoma. FTC is rarely multifocal and usually does not metastasize to the regional lymph nodes but tends to spread via the bloodstream to the lung and bones. An important histologic variant of FTC is the oncocytic (Hurthle cell, oxyphilic) follicular carcinoma composed of eosinophilic cells replete with mitochondria (summary by Bonora et al., 2010). For a general phenotypic description and a discussion of genetic heterogeneity of NMTC, see NMTC1 (188550).

Nonmedullary thyroid cancer (NMTC) comprises thyroid cancers of follicular cell origin and accounts for more than 95% of all thyroid cancer cases. The remaining cancers originate from parafollicular cells (medullary thyroid cancer, MTC; 155240). NMTC is classified into 4 groups: papillary, follicular (188470), Hurthle cell (607464), and anaplastic. Approximately 5% of NMTC is hereditary, occurring as a component of a familial cancer syndrome (e.g., familial adenomatous polyposis, 175100; Carney complex, 160980) or as a primary feature (familial NMTC or FNMTC). Papillary thyroid cancer (PTC) is the most common histologic subtype of FNMTC, accounting for approximately 85% of cases (summary by Vriens et al., 2009). PTC is characterized by distinctive nuclear alterations including pseudoinclusions, grooves, and chromatin clearing. PTCs smaller than 1 cm are referred to as papillary microcarcinomas. These tumors have been identified in up to 35% of individuals at autopsy, suggesting that they may be extremely common although rarely clinically relevant. PTC can also be multifocal but is typically slow-growing with a tendency to spread to lymph nodes and usually has an excellent prognosis (summary by Bonora et al., 2010). Genetic Heterogeneity of Susceptibility to Nonmedullary Thyroid Cancer Other susceptibilities to nonmedullary thyroid cancer include NMTC2 (188470), caused by mutation in the SRGAP1 gene (606523); NMTC3 (606240), mapped to chromosome 2q21; NMTC4 (616534), caused by mutation in the FOXE1 gene (602617); and NMTC5 (616535), caused by mutation in the HABP2 gene (603924). A susceptibility locus for familial nonmedullary thyroid carcinoma with or without cell oxyphilia (TCO; 603386) has been mapped to chromosome 19p.