Therapy

The predicted prognosis of patients with neuroendocrine tumors influences therapy. Treatment modalities are numerous, including diverse surgical procedures, chemotherapy, arterial embolization, hormone antagonists (somatostatin), and cytokines (interferon-a). Surgery is the treatment of choice in early-stage tumors to remove the primary tumors and locoregional lymph nodes. Operations depend on tumor location, tumor size, and multicentricity. Tumor location is the most important factor and is strongly correlated with tumor size. Therefore, the surgical procedures are discussed according to the location of the tumors.

Besides the presence of lymph node involvement, tumor histology determines the prognosis of bronchial neuroendocrine tumors. Atypical tumors have a worse prognosis. The tumor histology and tumor grading are obtained in only about 70% of tumors by bronchoscopy and bronchial lavage. Magnetic resonance imaging and CT scanning are used to identify these tumors as well as delineate tumor growth and identify lymph node metastases. Because locoregional tumor spread is encountered in one third of patients, radical resection is mandatory. Tumor-free margins are essential, and lymph node dissection should be performed. On the other hand, surgery should save as much of parenchyma as possible. Therefore, lobectomy with or without bronchoplasty should be the procedure of choice and pneumonectomy the exception. Bronchoscopic removal with laser coagulation should be reserved for unfit and high-risk patients.1'26

Thymic neuroendocrine tumors are extremely rare tumors and often arise with local invasion and paraneoplastic syndromes. Thus, the aims of surgery are to resect the tumor radically and to relieve paraneoplastic symptoms. Radical resection should be performed even in the presence of perithymic or vascular invasion followed by adjuvant radiation therapy. For patients with MEN 1 and primary hyperparathyroidism, prophylactic upper thymectomy should be done during neck exploration because supernumerary parathyroid glands are found in 15% to 20% of these patients and it also removes the site where thymus tumors may develop (especially in men).52,53

In gastric neuroendocrine tumors, surgery may be indicated, depending on their pathogenesis. For solitary or multiple gastric tumors in the presence of hypergastrinemia and ECL cell hyperplasia, limited surgical procedures may be justified. They include endoscopic removal of tumors or antrectomy to remove the source of gastrin. There is, however, a certain risk of tumor recurrence despite the return of serum gastrin to normal. For other gastric neuroendocrine tumors, radical resection with gastrectomy and lymphadenectomy should be performed.54

Duodenal neuroendocrine tumors are extremely rare tumors that may contain and secrete calcitonin or somatostatin and are often found as polypoid tumors by endoscopy. Endoscopic removal is justified because the tumors are small and the depth of invasion can be assessed by endolu-minal ultrasonography. Full-thickness wall excision or resection is necessary for tumors over 4 cm in diameter. The management of these lesions is determined on a case-by-case basis and dictated by presence of symptoms.19

Small bowel carcinoid tumors are the most common neuroendocrine tumors, with increasing frequency from the jejunum to the ileum. The most important prognostic parameter is the presence of lymph node metastases. There is also a good correlation of tumor size with locoregional tumor spread, with a critical size of 1.5 to 2 cm. Tumors of 1 cm in diameter or less, however, are capable of metastasis. Therefore, segmental resection with lymph node dissection is mandatory. Resection can relieve endocrine tumor symptoms even in the presence of distant metastases. The risk of short bowel syndrome, which is difficult to manage in combination with the carcinoid syndrome, should always be kept in mind by the surgeon.19'38'45,55'56

Appendiceal neuroendocrine tumors are mostly incidental findings, usually smaller than 1.5 cm in diameter. Generally, the tumors are located at the apex and seldom at the appendiceal base. As a rule, appendectomy is the standard procedure. If the tumor is located proximally or larger than 2 cm, additional partial resection of the cecum with lymph node dissection may be necessary. For larger tumors or suspicious lymph nodes, a right hemicolectomy is indicated.19'26 42

Neuroendocrine tumors of the colon show a decrease in frequency from the right to the left colon. Tumor size is strongly correlated with the incidence of lymph node involvement, with a critical diameter of about 1.5 to 2 cm. Most of the tumors are larger, so lymphatic tumor spread is to be expected. Surgical resection should include the lymphatic drainage similar to that for adenocarcinomas.19'26 57

Rectal neuroendocrine tumors are generally very small and rarely metastasize. Good access by palpation and proctoscopy presumably leads to early diagnosis, so that in most cases endoscopic removal or fulguration is sufficient. For larger tumors between 1 and 2 cm or those with deeper infiltration, a transanal excision should be performed. Transanal endosonography may be particularly useful in this intermediate group to assess tumor extension. A more radical approach (low anterior resection with total mesorectal excision or abdominoperineal resection) is restricted to larger tumors with a higher risk of metastasis.19,58

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