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328a) A 51-year-old woman underwent left parotidectomy. Her parotid gland contained a well-circumscribed lesion that measured 2.0 cm in the greatest dimension. The slide shows a representative section of the tumor. Which one of the following options represents the MOST likely diagnosis?

Basal cell adenoma, solid type Basal cell adenoma, membranous type Basal cell adenoma, tubular type Basal cell adenoma, trabecular type Basal cell adenoma, tubulo-trabecular type

328b) Which one of the following clinical features does NOT distinguish this type of basal cell adenoma from the other types?

Equal male:female distribution Multifocality Coexistence with dermal cylindromas or trichoepitheliomas Loss of heterozygosity/mutation at 16q12-13 (involving the gene CYLD1) Increased propensity for malignant transformation

328c) Regarding the distinction between basal cells and myoepithelial cells of normal salivary glands, which of the following statements is FALSE?

In normal salivary glands, myoepithelial cells occur in the acinus and intercalated duct, whereas basal cells occur in the striated duct and excretory duct. Positive immunohistochemical staining for p63 is expected in and/or consistent with both myoepithelial cells and basal cells. Positive immunohistochemical staining for actin and calponin is expected in and/or consistent with both myoepithelial cells and basal cells. Positive immunohistochemical staining for high molecular weight keratins (CK5/6, 34βE12) is expected in and/or consistent with both myoepithelial cells and basal cells. Positive immunohistochemical staining for low molecular weight keratins (CK7, CK19, CAM5.2) is expected in and/or consistent with both myoepithelial cells and basal cells.

328d) Regarding the distinction between basal cell adenoma and pleomorphic adenoma, which of the following statements is TRUE?

Pleomorphic adenoma occurs most frequently in the parotid gland, whereas basal cell adenoma occurs most frequently in the submandibular gland. The sharp distinction of lesional cells from the surrounding hyaline stroma (rather than “streaming” or “blending” of lesional cells into a myxoid stroma) suggests a diagnosis of basal cell adenoma, rather than pleomorphic adenoma. The finding of sebaceous elements elsewhere within this lesion would suggest a diagnosis of pleomorphic adenoma (rather than basal cell adenoma). The finding of chondroid elements elsewhere within this lesion would suggest a diagnosis of basal cell adenoma (rather than pleomorphic adenoma). Positive nuclear immunohistochemical staining for beta catenin would suggest a diagnosis of pleomorphic adenoma, rather than basal cell adenoma.

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• The World Health Organization classification system recognizes several different types of basal cell adenoma. The membranous type displays thick hyaline material between clusters of lesional cells (as in this case). The solid type consists of variably sized sheets and/or nests that show prominent cellular palisading. The tubular type contains prominent ductal structures. The trabecular type forms cellular strands and cords. The tubulo-trabecular type shows admixed features of the tubular and trabecular types.

• The membranous type of basal cell adenoma can be associated with the Brooke-Spiegler syndrome, which occurs due to loss of heterozygosity or mutation at 16q12-13 (involving the CYLD1 gene). This syndrome also includes dermal cylindromas and trichoepitheliomas.

• Unlike the other types of basal cell adenoma, the membranous type shows equal male:female distribution (the other types occur more frequently in women), and is more likely multifocal, and more likely to recur following surgical resection.

• Malignant transformation is exceedingly rare for basal cell adenoma of any type. The reported cases have not involved basal cell adenoma of membranous type.

• Several features of basal cell adenoma may facilitate distinction between this lesion and pleomorphic adenoma. These features include a sharp distinction between lesional cells and the surrounding hyaline stroma, the presence of sebaceous (rather than chondroid) metaplastic elements within the lesion, and positive nuclear immunohistochemical staining for beta catenin.

de Araujo VC: Basal cell adenoma.In: Barnes L, et al. (eds): World Health Organization Classification of Tumours: Pathology and Genetics of Head and Neck Tumours. Lyon: IARC Press, 2005, pp 261-262.

Yu GY, Ubmuller J, Donath K: Membranous basal cell adenoma of the salivary gland: a clinicopathologic study of 12 cases. Acta Otolaryngol 1998;118:588-593.

Nagao T, Sugano I, Ishida Y, et al: Carcinoma in basal cell adenoma of the parotid gland. Pathol Res and Pract 1997;193:171-178.

Anatomic Pathology: Salivary Gland Pathology

328a) A 51-year-old woman underwent left parotidectomy. Her parotid gland contained a well-circumscribed lesion that measured 2.0 cm in the greatest dimension. The slide shows a representative section of the tumor. Which one of the following options represents the MOST likely diagnosis?

328b) Which one of the following clinical features does NOT distinguish this type of basal cell adenoma from the other types?

328c) Regarding the distinction between basal cells and myoepithelial cells of normal salivary glands, which of the following statements is FALSE?

328d) Regarding the distinction between basal cell adenoma and pleomorphic adenoma, which of the following statements is TRUE?

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