P232

 Definition

Cystadenocarcinoma is a rare malignant tumour characterized by predominantly cystic growth that often exhibits intraluminal papillary growth. It lacks any additional specific histopathologic features that characterize the other types of salivary carcinomas showing cystic growth. It is conceptually the malignant counterpart of the benign cystadenoma.

ICD-O code 8440/3

Synonyms

 Papillary cystadenocarcinoma, mucusproducing adenopapillary (non-epidermoid) carcinoma {224,679,2463}, malignant papillary cystadenoma {2133}, and low-grade papillary adenocarcinoma of the palate {38,1742,2784}.

 Epidemiology

There is no sex predilection. The average age of patients is 59 years; more than 70% are over 50 years of age {790}.

 Localization

About 65% occur in the major salivary glands and most of these arise in the parotid. Involvement of the sublingual gland is proportionately greater than of other benign or malignant tumours {790}. The buccal mucosa, lips, and palate are the most frequently involved minor gland sites.

Clinical features

Cystadenocarcinomas usually manifest as a slowly growing, compressible asymptomatic mass. Tumours of the palate may erode bone.

 Macroscopy

The tumours have multiple cystic spaces that are variable in size and often filled with mucin. They are grossly at least partially circumscribed and have ranged in size from 0.4-6 cm.

Histopathology

The tumours are usually well circumscribed but not encapsulated. Numerous haphazardly arranged cysts are evident that are partially filled with mucin, vary in shape and size, and have limited intervening fibrous connective tissue. Small solid neoplastic islands or duct-like structures may occur between the cysts or at the advancing front of the tumour. In about 75% of the cases the lumens of the cysts exhibit varying degrees of papillary proliferation. In either case, cell types that comprise the lining epithelium include, most often, small and large cuboidal, and columnar cells, but mucous, clear and oncocytic cells are occasionally noted. The columnar-rich tumours often predominate in the intraluminal papillary areas and account for their “gastrointestinal” appearance, but the cells usually fail to stain for neutral mucin. Although nucleoli are evident, the nuclei typically are uniformly bland and mitoses rare. However, a prerequisite for the diagnosis is that the cysts and smaller duct-like structures at least focally infiltrate the salivary parenchyma and surrounding connective tissue. The presence of ruptured cysts with haemorrhage and granulation tissue is common.

Differential diagnosis

 Distinction from cystadenoma may be difficult and relies largely on identification of infiltrative growth into salivary parenchyma or surrounding tissues. Review of multiple sections is often helpful. Low-grade mucoepidermoid carcinoma is typically cystic but, unlike cystadenocarcinoma, usually has a wide variety of cell types and areas that are more solid than cystic. The papillary cystic variant of acinic cell carcinoma has focal acinar differentiation and a greater degree of epithelial proliferation. Epidermoid differentiation in cystadenocarcinomas is rare.

Prognosis and predictive factors

Cystadenocarcinoma is a low-grade adenocarcinoma treated by superficial parotidectomy, glandectomy of submandibular and sublingual tumours, and wide excision of minor gland tumours. Bone resection is performed only when it is directly involved by tumour {411,535, 790,2350}. In a study of 40 patients with follow-up data, all were alive or had died of other causes, four suffered metastasis to regional lymph nodes, one at the time of diagnosis and one after 55 months, and three experienced a recurrence at a mean interval of 76 months {790}.