Salivary glands

• Epithelial or myoepithelial malignancy developing from primary or recurrent pleomorphic adenoma

• Identification of both malignant and benign components is essential for diagnosis; in cases where the benign component has been obliterated by carcinoma, a history of pleomorphic adenoma at the site must be documented
• 5% of pleomorphic adenomas undergo malignant transformation, with the highest risk associated with recurrent or longstanding pleomorphic adenoma
• Typical clinical presentation is a longstanding palpable mass in the parotid region that has undergone recent rapid growth
• Salivary duct carcinoma and adenocarcinoma NOS are the most frequently encountered malignant components; other malignant components can be myoepithelial carcinoma or epithelial myoepithelial carcinoma
• Main predictors of outcome are patient age, tumor diameter, degree of capsule invasion, histological subtype of malignant component and lymph node or distant metastases

• Most common presentation is palpable mass in parotid region (Ear Nose Throat J 2019;98:504)
• May present as a sudden increase in size of a preexisting lump, pain or facial paresis / paralysis
• Long history of a mass prior to sudden increase in size is common, suggesting that long delays in treatment of pleomorphic adenoma increase the likelihood of malignant transformation (Acta Oncol 2009;48:132)
• ≤ 25% of patients have a history of previously treated pleomorphic adenoma (Plast Reconstr Surg 2005;116:1206)
• Advanced cases may present with skin ulceration or dysphagia (Head Neck 2001;23:705)

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Contributed by Ruta Gupta, M.B.B.S., M.D.

• Routine use of frozen section for salivary gland tumors is not appropriate (Head Neck 2019;41:269)
• May be useful in some settings (e.g. in cases of facial nerve sacrifice to ensure negative nerve stump margin) (Head Neck 2019;41:269)

Contributed by Ruta Gupta, M.B.B.S., M.D.

• Carcinoma ex pleomorphic adenoma (see comment)
  • Comment: In large areas, the tumor shows a sclerotic nodule. Several infiltrative glands and ducts are seen extending from the periphery of this sclerotic nodule into the adjacent residual salivary gland and attached skeletal muscle. Occasional glands show internal cribriform architecture with Roman bridges and arches and resemble ductal carcinoma in situ of the breast. The glands are lined by cells with an apocrine appearance with apical snouts, moderate eosinophilic cytoplasm and enlarged nuclei with distinctive nucleoli. Mitoses are present. Multiple foci of lymphovascular involvement are present. Perineural involvement is seen. The tumor is present at the margin of resection. In addition, 5/25 lymph nodes in the accompanying neck dissection show metastatic carcinoma. History of a longstanding nodule in the region of the parotid gland with sudden increase in size and new onset facial palsy is noted. The clinical history and the morphologic features support a diagnosis of a carcinoma ex pleomorphic adenoma.

• Recurrent pleomorphic adenoma:
  • Commonly multinodular; may show numerous disconnected nodules with no obvious capsule, simulating invasion (Laryngoscope 2004;114:158)
  • History of incompletely resected or previously recurrent pleomorphic adenoma is a clue to the diagnosis
• Pleomorphic adenoma with pseudopodia:
  • Small protrusions of tumor beyond the tumor capsule, found in up to a quarter of cases and without clinical consequence unless incompletely excised (Laryngoscope 2001;111:2195, Cancer 1998;82:617)
  • Must not be confused with malignant transformation
• De novo carcinoma:
  • Identification of residual pleomorphic adenoma (or a history of recurrent / incompletely excised pleomorphic adenoma) is essential for diagnosis of carcinoma ex pleomorphic adenoma
  • PLAG1 and HMGA2 genetic aberrations are seen in carcinoma ex pleomorphic adenoma but not its malignant de novo counterparts (Hum Pathol 2015;46:26)
• Metastatic carcinoma:
  • History of other primary head and neck malignancy
  • Absence of pleomorphic adenoma component

Regarding carcinoma ex pleomorphic adenoma, which of the following statements is true?

1. Fine needle aspiration is a highly sensitive technique for the diagnosis of this entity
2. Malignant transformation is equally likely to occur in a primary pleomorphic adenoma as it is in recurrent pleomorphic adenoma
3. Not always possible to identify the preexisting pleomorphic adenoma macroscopically
4. Submandibular gland is the most common site of origin

C. It is sometimes not possible to identify the pleomorphic adenoma macroscopically or even microscopically; this is one of the reasons why thorough sampling is required. This is because the malignant component may overgrow and subsume the benign component. In such circumstances, a history of pleomorphic adenoma, particularly if longstanding or recurrent, is vital for correct diagnosis. Like pleomorphic adenoma, carcinoma ex pleomorphic adenoma arises most commonly in the parotid gland. Recurrent pleomorphic adenoma has a higher risk of malignant transformation than primary pleomorphic adenoma. Fine needle aspiration has low sensitivity in the diagnosis of carcinoma ex pleomorphic adenoma, largely due to sampling error.

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Reference: Carcinoma ex pleomorphic adenoma

A 57 year old man presents with right facial swelling and paralysis. Following appropriate workup, he undergoes surgical resection of the right facial mass. A representative histological image is provided above. Regarding his diagnosis, which statement is true?

1. Component on the left is commonly encountered in this entity
2. Molecular features of the cellular component are completely distinct from those of the paucicellular component
3. Paucicellular component on the right is irrelevant to the final diagnosis
4. Presence or absence of a complete capsule around the cellular component does not alter the patient’s prognosis

A. The correct diagnosis is carcinoma ex pleomorphic adenoma. The component on the left is morphologically identical to salivary duct carcinoma, the most common malignant component of carcinoma ex pleomorphic adenoma other than adenocarcinoma NOS. The component on the right is the preexisting pleomorphic adenoma, which is a requirement for diagnosis. PLAG1 and HMGA2 molecular aberrations are encountered in both pleomorphic adenoma and carcinoma ex pleomorphic adenoma. The presence of a tumor capsule is of paramount prognostic significance, as noninvasive or minimally invasive carcinoma ex pleomorphic adenoma is associated with excellent outcomes.

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Reference: Carcinoma ex pleomorphic adenoma