Pathology of the Head and Neck

Major and Minor Salivary Glands Chapter 5 159Table 5.4. Metastases to the parotid gland, adapted from Gnepp [82]Location of primaryNumber of tumoursSkin of head and neck 422 (53.8%)Upper aero-digestive tract (mouth, nose, sinuses, pharynx) 63Eye (conjunctiva, lacrimal gland) 6Thyroid 5Head, not otherwise specified 4Central nervous system 4Submandibular salivary gland 1Lung 28Kidney 23Breast 19Colorectal 7Prostate 4Skin, distant 3Stomach 2Uterus 1Pancreas 1Total, distant sites 88 (11.2%)Skin, not otherwise specified 108Unknown primary site 84virus, and viral genomes can be detected in the malignantcells [89].There is a marked histological similarity to undifferentiatednasopharyngeal carcinoma, which has alsobeen linked to Epstein-Barr virus. Microscopic examinationshows syncytial groups of large epithelialcells with vesicular nuclei and prominent nucleoli,intimately mixed with lymphocytes and plasma cells,sometimes with germinal centre formation. Mitoticfigures are often numerous. At times, the epitheliumis difficult to identify, but it can be highlighted by cytokeratinmarkers. The most important differential diagnosisis a metastasis from a nasopharyngeal primary,which can present as a parotid mass [231], or possiblyvery poorly differentiated squamous carcinoma ofusual type originating in the skin or upper aerodigestivetract. The outcome is surprisingly good for suchan aggressive-looking carcinoma, and the 5-year survivalrate is 60%.5.9.14 Small Cell CarcinomaICD-O:8041/3Small cell carcinoma (SCC) is unlikely to be a singleentity, as electron microscopy reveals that some neoplasmsshow neuroendocrine differentiation, whilstothers have squamous and ductal features not apparenthistologically [15, 118], and occasionally both patternsare evident in the same tumours. Some neoplasmscalled small cell carcinoma may in fact be primaryprimitive neuroectodermal tumours [44]. They are seenmore often in men, and the mean age is 56 years (range5–86) [62]. The microscopic appearance may be similarto small cell carcinoma of the lung or Merkel cell carcinomaof the skin. Both comprise solid sheets, nests andcords of closely packed cells; the difference is in the cellsize – small and dark cells in the former, slightly largerand with pale chromatin in the latter.Immunohistochemistry shows positive staining forchromogranin, synaptophysin, neuron-specific enolaseand CAM5.2, often with paranuclear dots in bothtypes. However, immunohistochemistry for cytokeratin20 seems to identify two subtypes of small cell carcinoma:CK 20− lung cell type and CK 20+ Merkel celltype carcinoma. A recent study by Nagao et al. [148]showed that CK 20+ small cell carcinomas of the salivaryglands have a better prognosis than CK 20− cases.This suggests that staining for CK 20 should beperformed in SCC as the results may have prognosticvalue [148]. The differential diagnosis includes metastasisfrom small cell carcinomas of the lung and thismust be excluded before a primary small cell carcinomacan be said to be of salivary origin. Lymphomasand primary primitive neuroectodermal tumours ofthe salivary glands [44, 105] may be somewhat similarmorphologically, and can be excluded immunohistochemically.