Basal cell adenocarcinoma

Definition

 Dominated by basaloid epithelial cells, basal cell adenocarcinoma is cytologically and histomorphologically similar to basal cell adenoma but is an infiltrative epithelial neoplasm with potential for metastasis.

ICD-O code 8147/3

 Synonyms Basaloid salivary carcinoma, carcinoma ex monomorphic adenoma, malignant basal cell adenoma, malignant basal cell tumour, and basal cell carcinoma {159, 408,698,1163,1340,1576}. Tumours in infants reported as basal cell adenoma/ carcinoma or hybrids are best classified as sialoblastomas.

 Epidemiology

There is no sex predilection. The average age of patients is 60 years, and only adults have been affected {668,673, 1576,1792,2726}.

 Localization

Over 90%, of these tumours occur in the parotid gland, and they are rare in the minor salivary glands of the oral cavity {668,673,2703}.

Clinical features

Rarely, patients complain of pain or tenderness; most tumours are asymptomatic except for swelling. The duration of tumours before excision ranges from weeks to years. Similar to some patients with basal cell adenomas, patients with basal cell adenocarcinomas may have a diathesis of multiple skin adnexal tumours and parotid basal cell adenocarcinomas {65,668,673,1163, 1576}.

Macroscopy

 Basal cell adenocarcinomas most frequently occur in the superficial (lateral) lobe of the parotid gland. The cut surface has variable coloration of grey, tan-white, or brownish. The texture is homogeneous although some tumours are focally cystic. They are unencapsulated, but some tumours appear well-circumscribed while others are obviously infiltrative.

Histopathology

Basaloid epithelial cells, which vary from small, dark cells to larger, paler stained cells, form histomorphologic patterns that are described as solid, membranous, trabecular and tubular. A solid pattern, in which variable sized and shaped nests are separated by thin septa or thick bands of collagenous stroma, is most frequent. In the membranous type, tumours produce excessive amounts of eosinophilic, hyalinized basal lamina material that forms intercellular droplets and peripheral membranes. Interconnecting bands of basaloid cells characterizes the trabecular growth pattern. In the tubular type, there are luminal spaces among the basaloid cells. There are foci of squamous differentiation in some tumours. The nuclei of tumour cells along the interface with the collagenous stroma are often palisaded. The degree of cytologic atypia and the number of mitotic figures varies from one tumour to another but is often quite minimal. Infiltration of tumour cells into parotid parenchyma, dermis, skeletal muscle, or periglandular fat distinguishes basal cell adenocarcinoma from basal cell adenoma. Vessel or peripheral nerve invasion is evident in about a fourth of the tumours. Immunoprofile Immunohistochemical staining is variable among tumours. Tumour cells are reactive for cytokeratins and often focally reactive for S100 protein, epithelial membrane antigen, and carcinoembryonic antigen. Limited reactivity for smooth muscle actin and vimentin supports myoepithelial differentiation of some cells {2097,2793}.

Precursor lesions

 Most basal cell adenocarcinomas probably develop de novo, but some arise by malignant transformation in basal cell adenomas {1576,1792}.

 Genetics

 Cytogenetics Chromosomal gains at 9p21.1-pter, 18q21.1-q22.3, and 22q11.23-q13.31 as well as losses at 2q24.2 and 4q25-q27 have been described {2612}. The gain at 22q12.3-q13.1 is described as also common in adenoid cystic carcinoma. Molecular genetics A study of two familial cases and two sporadic basaloid tumours for alterations at the 16q12-13 regions showed high frequency (80%) of LOH in both sporadic and familial basaloid tumours and dermal cylindromas of the familial cases. The minimally deleted region contained the CYLD gene. This study indicates that these tumours share the same alterations as dermal cylindromas and implicates the CYLD gene in their development {437}.

Prognosis and predictive factors

While they are locally destructive and often recur, basal cell adenocarcinomas only occasionally metastasize, and death of patients is rare {408,673,698,1163, 1340,1576,1792,1799}. Ki-67 and PCNA indices are low {782,2097}.