Pathology of the Head and Neck

160 S. Di Palma · R.H.W. Simpson · A. Skalova · I. Leivo5High-grade transformation is a rare but well-establishedevent in several primary low-grade salivary carcinomas,and usually heralds a more aggressive clinicalcourse. Examples have been described in acinic cell[51, 95, 154, 213], adenoid cystic [32, 140], epithelialmyoepithelial[2, 73, 186], mucoepidermoid [146] andpolymorphous low-grade adenocarcinoma [160, 191],as well as malignant myoepithelioma [156]. In eachcase, the diagnoses of high-grade change were basedon histopathological criteria, especially increased mitoticand proliferation rates. Most of the transformedcomponents were poorly differentiated adenocarcinomas,but some of those in adenoid cystic and epithelial-myoepithelialcarcinomas showed myoepithelialfeatures. The processes underlying dedifferentiation ofsalivary neoplasms remain to be established, but previousradiotherapy may have been important in some ofthe AdCCs [32] and PLGAs [160]. In general, no definitefactors in the progression of low-grade to highgradecarcinomas have been identified at a molecularlevel [208]; for example, there is conflicting evidenceregarding p53 mutations, which might have been involvedin a single case of transformed AdCC [32], butwas not a factor in dedifferentiated acinic cell carcinomas[51, 95].5.9.16 MetastaticMalignanciesFigs. 5.53, 5.54. Endodermal sinus tumour of the parotid gland.Positive staining for placental alkaline phosphatase (PLAP) is essentialto confirm the diagnosis. Courtesy of Dr. Isabela Wernicke[211]5.9.15 Higher Grade Changein CarcinomasMetastases to the major glands and the intraparotidlymph nodes constitute approximately 10% of all salivarycarcinomas [82]; the exact figure varies fromstudy to study depending on local factors such as differentincidences of particular cancers. For example,Bergensen et al. [18] in Australia reported that metastasesconstituted 72% of all malignancies, resultingfrom the high incidence of skin cancer. In an AFIP seriesand literature review in 1991 of 785 parotid metastases[82], 64% were found to have originated from thehead and neck region (including the skin), 11% fromdistant sites and 25% from an unknown primary. Ofthe distant sites, lung, kidney and breast accounted formore than four-fifths (Table 5.4); only four cases werefrom the prostate, but it is perhaps under-recognised[195]. Metastases to the submandibular glands are lesscommon than to the parotids, but are more likely to befrom distant sites [226].Microscopically, metastases in the salivary glandscan resemble almost any primary tumour, so that forexample, mammary duct carcinoma is morphologicallyidentical (but immunohistochemically different) tosalivary duct carcinoma (see Sect. 5.9.9). Similarly, renalcell carcinoma is part of the differential diagnosisof any clear cell tumour of the salivary glands, and examplesof prostate carcinoma have been mistaken foracinic cell carcinoma [195]. Immunohistochemistry isof some value, and can identify prostate and thyroidprimaries and melanoma with a reasonable degree ofaccuracy. Unlike most primary malignant salivary tumours,renal cell carcinomas are usually negative withcytokeratin 7; in contrast, CD10 stains most kidneycarcinomas, but is only positive in salivary tumourswith myoepithelial differentiation. However, the possibilityof metastasis is still best confirmed or excludedby imaging techniques of the kidneys.