It is the most frequent type of NEC in the larynx, constituting 54% of all laryngeal neuroendocrine neoplasms, with approximately 300 cases described in the literature [106, 242].
Similar to other types of NEC, MD-NEC is more common in males, with a wide age range from 20 to 83 years. The majority of patients are heavy smokers. It arises mostly in the supraglottic region. Hoarseness and dysphagia are the most common symptoms; 20-30% of patients also experience pain [19, 243]. MD-NEC is rarely associated with carcinoid syndrome . Some pa
tients with MD-NEC have an elevated level of the serum calcitonin [23, 338].
Grossly, it presents as a submucosal nodule or as a polypoid lesion measuring up to 4 cm in diameter (average 1.6 cm), with or without surface ulceration.
Microscopically, the tumour grows in rounded nests, trabeculae, cords, ribbons and glandular structures; the tumour cells are round, with round nuclei and a moderate amount of cytoplasm, which is slightly eosinophil-ic or occasionally oncocytic. Mucin production may be present .
In contrast to WD-NEC, cellular pleomorphism, increased mitotic activity and necroses are frequently present in MD-NEC. Vascular and perineural invasion may be present.
Immunohistochemically, MD-NEC usually expresses synaptophysin, cytokeratin, and chromogranin; they may also express CD56, calcitonin and carcinoembry-onic antigens, but rarely serotonin (Figs. 7.13) [97, 234, 242, 388].
Differential diagnosis includes paraganglioma, ad-enocarcinoma, other neuroendocrine carcinomas and medullary carcinoma of the thyroid gland.
The differentiation between paraganglioma and MD-NEC is important because the former usually behaves as a benign tumour, while the latter behaves as an aggressive tumour. The correct diagnosis is usually possible with the use of immunohistochemistry: MD-NEC expresses cy-tokeratin and carcinoembryonic antigen (CEA), while paraganglioma does not. Both tumours express markers of neuroendocrine differentiation [18, 242]. Adenocarci-noma can be distinguished from carcinoid by the absence of neuroendocrine markers. The presence of cellular pleo-morphism, increased mitotic activity and necroses helps to distinguish MD-NEC from WD-NEC.
Differentiation from thyroid medullary carcinoma may be difficult, especially when dealing with cervical metastases, as tumour cells in both medullary carcinoma and MD-NEC express calcitonin by immunohisto-chemistry. The most important distinguishing feature is the different locations of the primary tumours. Additional useful information may be obtained by measuring the serum level of CEA, which is elevated in meta-static medullary carcinoma of the thyroid, and normal in MD-NEC . The elevated serum level of calcitonin should not be considered as a reliable feature of medullary carcinoma, as it has been reported in patients with MD-NEC [92, 338].
Moderately differentiated NEC is an aggressive, potentially lethal tumour. Lymph node metastases have been reported in 43% of patients, cutaneous metastases in 22% and distant metastases in 44% of patients, mostly to the lungs, liver and bones [97, 234, 388].
Surgery is the treatment of choice. Neck dissection is also advised because of the high incidence of cervical lymph node metastases. Radiation and chemotherapy have not been effective . The 5- and 10-year survival rates are 48 and 30% respectively .
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