Parotid tumor and thyroid cancer. Simultaneous occurrence after irradiation of the neck in childhood

A case report of mucoepidermoid carcinoma of the parotid gland developing after radioiodine therapy for thyroid carcinoma

This is a report on a 19-year-old female who developed a low grade T2 N0 M0 mucoepidermoid carcinoma of the right parotid gland 3 years and 5 months after the post-operative treatment of 100 mCi of radioactive iodine (131I) for a papillary thyroid carcinoma. The parotid tumour appeared during the patient's pregnancy. There are few reports of salivary gland cancer developing after radioiodine therapy for thyroid carcinoma and it is hoped that this report may stimulate others to investigate this association further in order to clarify the risk of secondary malignancies after radioiodine therapy.

[Morphology of salivary gland diseases]

The human salivary glands represent a functional system with manifold responsibilities and interactions to the organism. The major and minor salivary glands show a common construction schedule consisting of an acinar functional system for the production of an enzyme- and mucin-containing primary saliva and a ductal functional system with manifold secretory, resorptive and regulatory responsibilities for the transport and the definitive composition of the saliva. The cyclic AMP and calcium iones localized in the glandular acini have an exceptional importance for the course of the secretory process. The neurohormonal control of the salivary secretion results by adrenergic and cholinergic transmitter substances. Moreover the secretory process shows a daily cycle combined with morphological alterations of the glandular cells (so called circadian structures). The fluid secretion of the salivary duct system (the output of sodium-, potassium- and chlorine-iones) represents an active energy-consumed transport process which will be regulated by several factors (autonomic nervous system, quantity of perfusion, hydrostatic pressure in the blood capillaries, transepithelial active transport by ATP-consumed pump systems). The striated ducts are the functional most important sector of the duct system for a rapid fluid- and electrolyte excretion. The terminal axons of the postganglionic sympathic and parasympathic neurits are characterized by spindle-shaped enlargements (varicosities) which contain neurosecretory granules. In the region of the acinar and intercalated duct cells a direct synaptic contact exists for the stimulation transmission, in the course of which the terminal axon contacts immediately with the effector cell by penetration of the basement membrane. The salivary glands form a part of the stabil tissues with reversible postmitotic cells in regard of the tissue regeneration. Under pathological conditions (inflammations, impediment of secretion fluid, radiation effects etc.) metaplasias and proliferations of the duct system arise with development of indifferent duct formations analogous to the type of an embryonal salivary gland. The terminal zone between intercalated and striated ducts represents an indifferent zone with large regeneratory potency. A special behaviour shows the myoepithelial cells which are developed as well to the outside of primitive embryonic duct buds as differentiated intercalated and striated ducts. Morphologically three types of diseases can be classified in the salivary glands: sialadenosis, sialadenitis and tumours.(ABSTRACT TRUNCATED AT 400 WORDS)