Testicular germ cell tumors (TGCTs) affect 1 in 500 men and are the most common cancer in males aged 15 to 40 in western European populations. The incidence of TGCT rose dramatically during the 20th century. Known risk factors for TGCT include a history of undescended testis (UDT), testicular dysgenesis, infertility, previously diagnosed TGCT, and a family history of the disease. Brothers of men with TGCT have an 8- to 10-fold risk of developing TGCT, whereas the relative risk to fathers and sons is 4-fold. This familial relative risk is much higher than that for most other types of cancer (summary by Rapley et al., 2000). Genetic Heterogeneity of Testicular Germ Cell Tumors A locus for testicular germ cell tumors (TGCT1; 300228) has been identified on chromosome Xq27. [from OMIM]

Mastocytosis, or mast cell disease, is a heterogeneous group of clinical disorders characterized by the abnormal accumulation of mast cells in various tissues, especially in the skin and hematopoietic organs. Mastocytosis usually appears in infancy or early adulthood. In most pediatric cases, the disease is limited to the skin, but it can be associated with systemic symptoms due to the release of mediators from mast cells, even when there is no systemic infiltration. It usually has a good prognosis, with substantial improvement or spontaneous resolution before puberty. In rare cases, the disease may remain active through adolescence as a systemic adult mastocytosis. Cutaneous mastocytosis is characterized by macules, papules, nodules, or diffuse infiltration of the skin, often associated with localized hyperpigmentation. Gentle rubbing of the lesions induces histamine release from mechanically activated mast cells, causing local wheals, erythema, and often pruritus, a phenomenon termed the 'Darier sign.' In contrast to childhood-onset mastocytosis, adult-onset mastocytosis often persists for the lifetime of the patient and is also more likely to be a severe and systemic disease involving numerous organs. In some cases, it is associated with a clonal hematologic non-mast-cell lineage disease, such as a myelodysplastic or myeloproliferative disorder. Adult-onset mastocytosis can also lead to the rare mast cell leukemia, which carries a high risk of mortality (summary by Bodemer et al., 2010 and Kambe et al., 2010). [from OMIM]

Gastrointestinal stromal tumors are mesenchymal tumors found in the gastrointestinal tract that originate from the interstitial cells of Cajal, the pacemaker cells that regulate peristalsis in the digestive tract. Approximately 70% of GISTs develop in the stomach, 20% in the small intestine, and less than 10% in the esophagus, colon, and rectum. GISTs are typically more cellular than other gastrointestinal sarcomas. They occur predominantly in patients who are 40 to 70 years old but in rare cases may occur in younger persons (Miettinen et al., 1999, 1999). GISTs are also seen as a feature in several syndromes, e.g., neurofibromatosis-1 (NF1; 162200) and GIST-plus syndrome (175510). [from OMIM]

Piebaldism is a rare autosomal dominant trait characterized by the congenital absence of melanocytes in affected areas of the skin and hair. A white forelock of hair, often triangular in shape, may be the only manifestation, or both the hair and the underlying forehead may be involved. The eyebrows and eyelashes may be affected. Irregularly shaped white patches may be observed on the face, trunk, and extremities, usually in a symmetrical distribution. Typically, islands of hyperpigmentation are present within and at the border of depigmented areas (summary by Thomas et al., 2004). [from OMIM]

A clonal expansion of myeloid blasts in the bone marrow, blood or other tissues. The classification of acute myeloid leukemias (AMLs) encompasses four major categories: 1) AML with recurrent genetic abnormalities; 2) AML with multilineage dysplasia; 3) Therapy-related AML; 4) AML not otherwise specified. The required bone marrow or peripheral blood blast percentage for the diagnosis of AML is 20% (WHO classification) [from NCBI]