ADENOID CYSTIC CARCINOMA: CLINICAL FEATURES, HISTOPATHOLOGY & TREATMENT
Author: Sanketh DS, MDS
Adenoid cystic carcinoma(AdCC) is a slow-growing, aggressive malignant neoplasm accounting for 10% of all tumors of the salivary glands. It was formerly called “cylindroma” due to its histological appearance but was subsequently termed AdCC by Spies in 1930.Case series report this tumor to be the 2nd most common malignant salivary gland tumor after mucoepidermoid carcinoma(MEC) although there are reports which say it is the 5th most common malignant tumor.
AdCC occurs in the both minor and the major salivary glands with 40-60% of the tumors occurring in the minor glands. Among the major glands, parotid and submandibular glands are most favoured with parotid being more common among the two. Among the minor glands, AdCC is most commonly found on the palate. Less commonly, sites such as lower lip, buccal mucosa, tongue and floor of mouth could also be involved. AdCC occurs predominantly among the older patients, usually ranging from 4th to 6th decades of life and has a slight female predilection.
AdCC usually presents as a slow growing mass followed by pain, which is a common and significant finding given the tendency of the tumor for perineural invasion. It may present with a low-grade, dull pain followed by numbness as the lesion advances. Parotid tumors may present with facial nerve paralysis. Palatal tumors may show a smooth or ulcerated surface. Overall, AdCC shows slow, relentless, persistent growth with mild pain and paraesthesia and a late onset of distant metastases to the lungs and bone.
AdCC is characterised by 3 different growth patterns namely, cribriform, tubular and solid, in different combinations and is classified based on the predominant pattern seen.
This is the most characteristic pattern of AdCC and is composed of variable sized islands of basaloid cells with interspersed cyst like spaces. The presence of cyst like spaces give a “Swiss-cheese” appearance to this pattern. These cyst-like spaces do not represent true ducts and may contain basophilic myxoid substance or an eosinophilic hyaline material. The islands may sometimes be surrounded by this hylanized material. These substances ultra-structurally represent glycosaminoglycans. The islands may occasionally harbour true ducts lined by cuboidal cells.
The basaloid cells are small and cuboidal with scanty cytoplasm and deeply basophilic nucleus. Pleomorphism is very mild and there are no mitotic figures.
The tubular pattern consists of small or elongated tubules/ducts in a hyalinzed stroma, lined by a single layer of ductal epithelial cells which is surrounded by single or multiple layers of basaloid cells.
The solid pattern consists of solid sheets or islands of basaloid cells with very few to no interspersed pseudocysts and ducts/tubules. Basaloid cells in the solid variant show cellular pleomorphism and mitotic figures. Coagulative necrosis may also be observed.
The tumors are graded according to their histopathological patterns as Grade I, II and III. Grade I tumors have a mixed cribriform-tubular pattern, no solid islands and bland cells with no pleomorphism.
Grade II tumors show a mixed cribriform-tubular pattern with <30% solid islands and they may show mild pleomorphism.
Grade III tumors are those with the solid pattern comprising more than 30% of the tumor. Pleomorphism, mitosis and necrosis may be observed.
TREATMENT AND PROGNOSIS
The 5 year survival rate of AdCC is around 60-75% but the 10 year survival rate decreases drastically to 30-54%. Distant metastasis to the lungs, bone and other soft tissue is common. Grade III tumors are clinically associated with large sized tumors and have the worst prognosis. Perineural invasion has reported to have little effect if any on prognosis of the tumor. Surgical resection of the tumor is the treatment of choice. The tumor has a high recurrence rate and 80-95% of the patients usually die after a long clinical course.
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Slide illustrating histopathology(cribriform pattern) of Adenoid cystic carcinoma:
Intermediate magnification micrograph of adenoid cystic carcinoma, abbreviated AdCC. H&E stain/Nephron/CC-BY-SA-3.0
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