Table 4. Common Genetic Syndromes Associated With Hamartomatous Polyps continued...
Another tumor suppressor gene on chromosome 18 is associated with progression of polyps to malignant form. Multiple colon carcinomas have been associated with neurofibromatosis type I and several other rare syndromes.
These tumors, like bronchial adenomas, may be benign or malignant and can involve the lining of the lung, large or small bowel, or liver.[107,108,109,110,111,112] Most lung lesions are benign; however, some metastasize.
Most carcinoid tumors of the appendix are discovered incidentally at the time of appendectomy, and are small, localized tumors; simple appendectomy is the therapy of choice.[114,115] For larger (>2 cm) tumors or tumors that have spread to local nodes, cecectomy or rarely, right hemicolectomy, is the usual treatment. It has become accepted practice to remove the entire right colon in patients with large carcinoid tumors of the appendix (>2 cm in diameter) or with tumors that have spread to the nodes; however, this practice remains controversial.
A MEDLINE search did not find any documented cases of childhood localized appendiceal carcinoid in children younger than 18 years with complete resection who relapsed. Treatment of metastatic carcinoid tumors of the large bowel or stomach becomes more complicated and requires treatment similar to that given for colorectal carcinoma. (Refer to the PDQ summary on adult Gastrointestinal Carcinoid Tumors for therapeutic options in patients with malignant carcinoid tumors.)
The carcinoid syndrome of excessive excretion of somatostatin is characterized by flushing, labile blood pressure, and metastatic spread of the tumor to the liver. Symptoms may be lessened by giving somatostatin analogs, which are available in short-acting and long-acting forms. Occasionally, carcinoids may produce ectopic ACTH and cause Cushing disease.
Gastrointestinal Stromal Tumors (GIST)
Gastrointestinal stromal tumors (GIST) are the most common mesenchymal neoplasms of the gastrointestinal tract in adults. These tumors are rare in children. Approximately 2% of all GIST occur in children and young adults;[122,123,124] in one series, pediatric GIST accounted for 2.5% of all pediatric nonrhabdomyosarcomatous soft tissue sarcomas. Previously, these tumors were diagnosed as leiomyomas, leiomyosarcomas, and leiomyoblastomas. In pediatric patients, GIST are most commonly located in the stomach and usually occur in adolescent females.[126,127]