Salivary glands
Primary salivary gland neoplasms - malignant
Polymorphous adenocarcinoma

Editor-in-Chief: Debra Zynger, M.D.
Bin Xu, M.D., Ph.D.

Topic Completed: 12 May 2020

Minor changes: 13 May 2020

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PubMed Search: Polymorphous adenocarcinoma[TI] salivary glands

Bin Xu, M.D., Ph.D.
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Cite this page: Xu B. Polymorphous adenocarcinoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/salivaryglandsPLGA.html. Accessed July 6th, 2020.
Definition / general
  • Polymorphous adenocarcinoma is an indolent salivary gland carcinoma characterized by cytologic uniformity and architectural diversity, predominantly affecting minor salivary glands, in particular the hard and soft palate
Essential features
  • Occurs in minor salivary glands predominantly, in particular the palate in approximately 60% of cases
  • Composed entirely of one cell type with pale nuclei and open chromatin
  • The term polymorphous refers to the architectural diversity, i.e. the tumors contains multiple architectural patterns
  • Characterized by molecular alteration of PRKD genes, in particular PRKD1 E710D hotspot mutations (Nat Genet 2014;46:1166, Mod Pathol 2020;33:65)
Terminology
  • Terminal duct carcinoma, lobular carcinoma, low grade papillary adenocarcinoma, cribriform adenocarcinoma of (minor) salivary gland, polymorphous low grade adenocarcinoma
ICD coding
  • ICD-O: 8525/3 - Terminal duct adenocarcinoma
  • ICD-10: C05.9 - Malignant neoplasm of palate, unspecified
Epidemiology
Sites
  • Most frequently occurs in the palate (in 49 - 87% of cases) (Am J Surg Pathol 2016;40:1526, Cancer 1999;86:207, Arch Otolaryngol Head Neck Surg 2010;136:385)
  • Other possible primary sites are minor salivary glands of upper aerodigestive tract, including oral cavity (e.g. floor of mouth, retromolar trigone, lip and lateral tongue), oropharynx (e.g. base of tongue and tonsil), sinonasal tract and nasopharyx
  • May occur in major salivary gland, in particular the parotid gland, in less than 5% of cases
Clinical features
  • Commonly presents with palpable mass
Diagnosis
  • Typically rendered in biopsy or resection specimens
Radiology description
  • No specific radiologic findings
  • CT and MRI are used preoperatively to establish the extent of disease and the presence of bone invasion
Radiology images

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CT

Prognostic factors
Case reports
Treatment
  • Surgical resection with appropriative margin is the primary curative treatment (Eur Arch Otorhinolaryngol 2018;275:1681)
  • Neck lymph node dissection may be performed for patients with a diagnosis of cribriform adenocarcinoma or with clinically positive lymph node(s)
  • Postoperative radiation therapy may be considered on an individual basis, especially for tumors with positive margins or perineurial invasion (Eur Arch Otorhinolaryngol 2018;275:1681)
  • Chemotherapy is in general reserved for patients with distant metastasis or nonoperable disease (Eur Arch Otorhinolaryngol 2018;275:1681)
Clinical images

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Submucosal mass involving maxilla

Palate nodule

Gross description
  • Typically presents as a submucosal white to beige, firm, lobulated nodule or mass with infiltrative border
Gross images

Contributed by Bin Xu, M.D., Ph.D.

Macroscopic appearance

Microscopic (histologic) description
  • Diagnostic criteria:
    • Cytologic uniformity: the tumor is composed entirely of one type of tumor cells characterized by monotonous pale nuclei with marked chromatin clearing resembling that of papillary thyroid carcinoma
    • Architectural diversity: showing highly variable architectural patterns of different proportions, including single filing arrangement, trabecular, tubular, reticular, papillary, solid and cribriform pattern
  • Targetoid arrangement and streaming of tumor cells and nests around nerves and vessels are common
  • Perineurial invasion is frequent, being seen in 60 - 75% of cases (Oral Surg Oral Med Oral Pathol 1991;71:469, Am J Surg Pathol 2016;40:1526)
  • Uncommon histologic features include: microcalcification, oncocytic changes, mucocytes and high grade transformation (defined as marked nuclear atypia, prominent mitotic activity and tumor necrosis) (Head Neck Pathol 2019;13:131)
  • Cribriform adenocarcinoma of salivary gland
    • Cribriform adenocarcinoma is currently considered by WHO classification as a variant of polymorphous adenocarcinoma (Chan: WHO Classification of Head and Neck Tumours, 4th Edition, 2017)
    • First described as a tumor with a high propensity to base of tongue/posterior tongue location and a high risk of nodal metastasis (Histopathology 1999;35:495)
    • Later reported in minor salivary glands outside of base of tongue and even major salivary gland (Am J Surg Pathol 2011;35:1168, Am J Surg Pathol 2016;40:1526, Mod Pathol 2020;33:65)
    • Shares the same cytologic features of optic clearing pale nuclei and immunohistochemistry profile as polymorphous adenocarcinoma
    • Characterized by lobulated architecture separated by fibrous septa and relatively uniformed solid, cribriform or microcystic architecture
      • Peripheral palisading, peripheral clefting and glomeruloid structures are common
Microscopic (histologic) images

Contributed by Bin Xu, M.D., Ph.D.

Infiltrative mass

Optical clearing of nuclei

Targetoid arrangement and perineural invasion

Papillary architecture

Cribriform architecture


Reticular pattern

Solid pattern

Oncocytic changes

Cribriform adenocarcinoma of salivary gland


S100

CK7

Virtual slides

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Polymorphous adenocarcinoma

Cytology description
  • Given that most tumors are located intraorally, fine needle aspiration cytology is rarely used for the diagnosis
  • Case reports show that this tumor typically contains uniform tumors cells with ground glass nuclei, scattered nuclear grooves and inconspicuous nucleoli
Cytology images

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Papanicolaou stain

Positive stains
Molecular / cytogenetics description
Molecular / cytogenetics images

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PRKD mutations and fusions

Sample pathology report
  • Palate, right, partial maxillectomy:
    • Polymorphous adenocarcinoma, 2.3 cm, margin uninvolved by carcinoma (see synoptic report)
Differential diagnosis
Board review style question #1

    Which underlying molecular alteration is a characteristic of this palate tumor?

  1. EWSR1-ATF1 fusion
  2. MYB-NFIB fusion
  3. PLAG1 fusion
  4. PRKD1 E710D hotspot mutation
Board review answer #1
D. PRKD1 E710D hotspot mutation. This is a polymorphous adenocarcinoma.

Reference: Polymorphous adenocarcinoma

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Board review style question #2
    Which of the following statements about polymorphous adenocarcinoma is true?

  1. It is a biphasic salivary gland carcinoma showing ductal (epithelial) and myoepithelial differentiation
  2. It is the most common salivary gland carcinoma originated from the palate
  3. It is the most common salivary gland neoplasm originated from the palate
  4. It most frequently occurs in the palate
Board review answer #2
D. It most frequently occurs in the palate

Reference: Polymorphous adenocarcinoma

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