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Pathology & Laboratory Medicine

URMC / Pathology & Laboratory Medicine / Education / Case of the Month / Case 38: Painless Face Nodule / Diagnosis

 

Diagnosis and Discussion

Diagnosis

Pleomorphic adenoma.

Discussion

Pleomorphic adenoma is the most common benign neoplasm of the salivary glands and frequently occurs in the parotid gland. Morphologically, it is a benign epithelial tumor that shows both epithelial and myoepithelial elements mixed with mesenchymal myxoid-, mucoid-, or chondroid-appearing material. Occasionally, pleomorphic adenoma can present as a superficial lesion, as the parotid gland tissue may extend superficially or accessory salivary gland tissue may be present. Skin based adnexal tumors, in particular cutaneous mixed tumor show significant histologic overlap with pleomorphic adenoma.

PLAG1 is an abbreviation for pleomorphic adenoma gene 1, which is a zinc finger transcription factor. Rearrangements in the PLAG1 gene lead to overexpression and have been described in approximately 50% of pleomorphic adenomas. Often PLAG1 rearrangement is associated with high cellularity and little chondro-myxoid stroma in pleomorphic adenomas. PLAG1 rearrangements can also occur in higher grade salivary gland lesions such as carcinoma ex pleomorphic adenoma. More recently PLAG1 rearrangements were also described in a subset of skin based adnexal tumors, such as cutaneous mixed tumor.

Differentiating salivary gland lesions from skin adnexal tumors can be very challenging. In addition, differentiating benign pleomorphic adenoma from a carcinoma may be challenging in small biopsy samples and relies on the presence of cytologic atypia, mitoses, and necrosis.

In our patient, due to the location of the biopsied lesion in the deep soft tissue of the malar cheek and the benign cytologic appearance, a pleomorphic adenoma of the parotid gland was favored.

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References

Bahrami A, Dalton JD, Krane JF, et al. A Subset of Cutaneous and Soft Tissue Mixed Tumors Are Genetically Linked to Their Salivary Gland Counterpart. Genes Chromosomes Cancer 2012;51:140–148.

Matsuyama A, Hisaoka M, Hashimoto H. PLAG1 expression in cutaneous mixed tumors: an immunohistochemical and molecular genetic study. Virchows Arch. 2011;459:539–545.

Nelson, Brenda L. Pleomorphic Adenoma. Head and Neck Section. https://app.expertpath.com/

Wenig, Bruce M. Atlas of Head and Neck Pathology . Third edition. Philadelphia, Pennsylvania: Elsevier, 2016. Print.