The presumed mechanism is neuroendocrine cell proliferation stimulated by elevated gastrin levels. The peak incidence of carcinoids is the sixth decade. No other sex, racial or geographic preference. These tumors are fairly well circumscribed but not encapsulated, white or pale yellow tan, and very firm due to a marked desmoplastic reaction. The overlying mucosa is usually intact, and the tumor is seen as a submucosal smooth nodule.
Large lesions can ulcerate the mucosa or penetrate the serosa.
Virtually all symptomatic carcinoids are found to have signifcant liver metastases at the time of discovery. The nomenclature of Carcinoid tumors is in flux, with some restricting the term to those tumors showing the classical histologic patterns described for Carcinoids, while other prefer to use the term neuroendocrine tumor for all tumors showing a predominant neuroendocrine expressiopn. The most striking feature is the bland monotous uniform appearance of the tumor without pleomorphism or mitotic activity. As with other endocrine tumors, prediction of malignant behavior can not be made on the histologic appearance. Carcinoids are slow growing low grade malignant tumors most of which do not metastasize and are asymptomatic at death.