Page 553 - Textbook of Pathology, 6th Edition

Malignant Mixed Tumour 537
Malignant mixed tumour comprises three distinct
clinicopathologic entities:
Carcinoma arising in benign mixed salivary gland tumour
(carcinoma ex pleomorphic adenoma);
Carcinosarcoma; and
Metastasising mixed salivary tumour.
Carcinoma ex pleomorphic adenoma is more common
while the other two are rare tumours. Approximately 2 to
5% of pleomorphic adenomas reveal areas of frank
malignancy. The slow-growing adenoma may have been
present for a number of years when suddenly it undergoes
rapid increase in its size, becomes painful and the individual
may develop facial palsy. Malignant transformation occurs
in later age (6th decade) than the usual age for pleomorphic
adenoma (4th to 6th decades). It may occur in primary
tumour but more often occurs in its recurrences.
Figure 19.17 Adenoid cystic carcinoma. It shows nests of tumour
MORPHOLOGIC FEATURES. Grossly, the tumour is cells having fenestrations containing basophilic material.
poorly-circumscribed with irregular infiltrating margin.
Cut section may show haemorrhages, necrosis and cystic Adenocarcinoma
degeneration. Adenocarcinoma of the salivary gland does not differ from
Microscopically, besides the typical appearance of adenocarcinoma elsewhere in the body. It may have some
pleomorphic adenoma, malignant areas show cytologic variants such as mucoid adenocarcinoma, clear-cell CHAPTER 19
features of carcinoma such as anaplasia, nuclear adenocarcinoma and papillary cystadenocarcinoma.
hyperchromatism, large nucleolisation, mitoses and
evidence of invasive growth. All types of usual salivary Epidermoid Carcinoma
gland carcinomas (described below) may develop in
pleomorphic adenoma. This rare tumour has features of squamous cell carcinoma
with keratin formation and has intercellular bridges. The
Adenoid Cystic Carcinoma (Cylindroma) tumour commonly infiltrates the skin and involves the facial
nerve early.
This is a highly malignant tumour due to its typical infil-
trative nature, especially along the nerve sheaths. Adenoid
cystic carcinoma is histologically characterised by cribriform Undifferentiated Carcinoma
appearance i.e. the epithelial tumour cells of duct-lining and This highly malignant tumour consists of anaplastic epithe-
myoepithelial cells are arranged in duct-like structures or lial cells which are too poorly differentiated to be placed in
masses of cells, having typical fenestrations or cyst-like any other known category. The Oral Cavity and Salivary Glands
spaces and hence the name ‘adenoid cystic’. These cystic
spaces contain PAS-positive basophilic material (Fig. 19.17).
Miscellaneous Malignant Tumours
Acinic Cell Carcinoma Some rare malignant tumour of epithelial and mesenchymal
origin are melanoma, sebaceous carcinoma, undifferentiated
This is a rare tumour composed of acinic cells resembling carcinoma, lymphoma, fibrosarcoma and leiomyosarcoma
serous cells of normal salivary gland. These cells are arranged and are similar in morphology to such tumours elsewhere
in sheets or acini and have characteristic basophilic granular in the body. Besides, metastatic involvement of major salivary
cytoplasm. The degree of atypia may vary from a benign glands or the adjacent lymph nodes is common, especially
cytologic appearance to cellular features of malignancy. from epidermoid carcinoma and malignant melanoma.

q