Histopathology

The main feature is both true adenocarci-noma and SCC. The two components occur in close proximity, but they tend to be distinct and separate, not intermingled as in mucoepidermoid carcinoma. The SCC component can present either as in-situ or as an invasive SCC {43}. The adenocarcinomatous component tends to occur in the deeper parts of the tumour. It consists of tubular structures that give rise to "glands within glands". Mucin production is typically present, either intraluminal or intracellular, and can appear as signet ring cells. However, mucin is not a requirement for the diagnosis in the presence of true glanduloductal formation. Metastases may display both components; one usually predominates.

Immunoprofile

There is positive staining for high-molecular weight cytokeratin in both components. The glandular component expresses CEA and low MW cytoker-atins: specifically, CK7 is positive, and CK20, is negative {43,1646}.

Electron microscopy

Features of both squamous and adeno-carcinomatous differentiation are found {231,1190}.

DNA ploidy

A high prevalence of aneuploidy has been demonstrated {43}.

Differential diagnosis

This includes mucoepidermoid carcino-

Fig. 3.24 Adenosquamous carcinoma. A squamous cell carcinoma in-situ (upper-left) appears in continuity with gland-like formations (bottom-right).

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Fig. 3.25 Adenosquamous carcinoma of the larynx. A Blended adenocarcinoma and squamous cell carcinoma within a single tumour mass. B Mucin-filled epithelial cells are part of areas of squamous differentiation.

Fig. 3.26 Adenosquamous carcinoma. A Positive imunohistochemical reaction for CK7 in areas with glandular differentiation. B Mucicarmine positive secretion in the cytoplasm of a single signet ring cell showing a markedly atypical nucleus.

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