Adenosquamous Carcinoma

ICD-O:8560/3

Adenosquamous carcinoma (ASC) is a rare malignant epithelial tumour characterised by the presence of both SCC and adenocarcinoma, and aggressive behaviour. It occurs in various sites, such as the pancreas [68], lung [262], uterine cervix [132], prostate [310], stomach [44] and breast [305]. In the head and neck, it was first reported by Gerughty et al. [131] who described a series of 10 patients with nasal, oral and laryngeal ASC.

Since then, over 150 cases of ASC of the head and neck have been reported; the most frequent site of occurrence is the larynx [8, 83, 124, 192], followed by the nose and paranasal sinuses [8, 245], oral cavity [8, 192, 258, 317, 385], upper lip [234], nasopharynx [234], oropharynx [234] and hypopharnyx [83, 234, 313].

The histogenesis of the ASC has not yet been completely elucidated. Some authors have suggested that it originates from the salivary and/or mucoserous glands [131] while others favour a surface epithelial derivation or a combined glandular and surface epithelial derivation [83]. However, it is becoming increasingly accepted that the basal cells of the surface squamous epithelium, which are capable of divergent differentiation, are the sole origin of ASCs [8, 258, 264, 317].

Aetiology has not been defined, but cigarette smoking and alcohol consumption probably play an important role in the pathogenesis of ASCs, similar to other types of SCC in the upper aerodigestive tract [8, 131, 192].

Adenosquamous carcinomas do not differ macroscopi-cally from conventional SCCs. Microscopically, they are characterised by the presence of both adenocarcinoma and SCC. The two components occur in close proximity, but are generally distinct and separate, and are not closely intermingled as in the mucoepidermoid carcinoma. The SCC component can present either as an in situ or as an invasive SCC, manifesting intercellular bridges, keratin pearl formation or dyskeratosis. The adenocar-cinomatous component is usually located in the deeper parts of the tumour; it consists of tubular, alveolar or ductular structures (Fig. 1.19).

Fig. 1.19. Adenosquamous carcinoma: squamous cell carcinoma in situ and the adenocarcinomatous component in the deeper part of the tumour. The two components are in close proximity, though separate

The presence of intracytoplasmic mucin can be demonstrated by special techniques, such as PAS, Alcian blue and Mayer mucicarmine. Necroses and mitoses are common [8, 192].

Immunohistochemistry has demonstrated positive staining for cytokeratins with high molecular weight in both the SCC and the adenocarcinomatous components, and positive staining for carcinoembryonic antigen (CEA) and cytokeratins with low molecular weight in the adenocarcinomatous component [8, 234].

By electron microscopy, features of both squamous and adenocarcinomatous differentiation have been demonstrated [41, 164].

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