This is a malignancy of the parafollicular cells of the thyroid.
This is a relatively uncommon thyroid carcinoma accounting for about 5% of thyroid malignancy. Both sexes are equally affected and the age of onset is variable. Aggressiveness is intermediate between that of well- differentiated and anaplastic lesions. About 80-90% of cases are sporadic; these usually affect adults and are unilateral. The other cases are familial, with an autosomal dominant inheritance; these tumours are typically bilateral and multifocal.
The medullary carcinoma arises from the parafollicular or C-cells of the thyroid which are of neural crest origin and form part of the APUD system. Calcitonin levels tend to be elevated and diagnostic. Levels of serum serotonin, ACTH and other peptides may also be raised. Spread to both regional lymph nodes and distant metastases to bone, liver and lung are common.
Diarrhoea and facial flushing are associated with medullary carcinomas of the thyroid.
20% of cases occur as part of the MEN-II syndrome.
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