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The treatment and prognosis of islet cell tumors vary, depending on both the size and the function of the lesion. Larger lesions more commonly demonstrate local invasion, vascular invasion, and distant metastases and are usually clinically silent tumors or associated with less recognizable symptoms. They are malignant in 50%-100% of cases (3,6,61). Non-insulin-producing lesions are commonly accompanied by metastatic disease at the time of diagnosis. Gastrinomas demonstrate metastasis in approximately one-half of patients at the time of initial diagnosis (10). Glucagonomas are malignant in over 60% of patients; the 5-year survival rate of these patients is 55% (12,20). Somatostatinomas demonstrate metastatic disease in 70% of patients at initial diagnosis (64); the average survival time of these patients is less than 2 years (27,64). Vipomas are malignant in 50%-80% of cases (4,20,64). Almost all ACTH-producing tumors behave malignantly and have metastases at the time of diagnosis (61). Insulinomas, on the other hand, behave in a benign fashion in over 90% of sporadic cases (ie, those not associated with MEN type I) (8,18,64).
Insulinomas are the most amenable to surgery at the time of presentation. In addition, surgery is usually curative, which is fortunate since there is no effective medical treatment for hyperinsulinemia. Gastrinomas, on the other hand, are frequently multiple, commonly metastatic, and not easily localized; thus, surgery is curative in only 30% of patients with sporadic gastrinoma (65). However, medical therapy may control the symptoms of Zollinger-Ellison syndrome.
Somatostatin analogues, such as octreotide, and agents directed at vasoactive intestinal polypeptide receptors have great appeal as delivery vehicles for the treatment of pancreatic endocrine tumors with radiation (66). Theoretically, this technique should prove effective in treating malignant and metastatic lesions. These areas are currently under investigation (31,66).
The prognosis and cure rate for patients with MEN type I syndrome and islet cell tumors is universally poor. Islet cell tumors in these patients are usually multiple and malignant. In patients with MEN type I and the Zollinger-Ellison syndrome, surgical cure is not possible. Surgical cure is possible in patients with MEN type I and insulinomas, but recurrences are frequent (18,19).
Treatment and Prognosis