HIGH YIELD: Mucoepidermoid Carcinoma

High Yield Info. No fluff. Here's some of the key features to know (for the boards)...

GENERAL INFO

Most common... malignant tumor of salivary glands

Most common... radiation-induced neoplasm

A "Muco-Ep" is basically is a tumor that has both adeno/glandular (MUCOus) + squamous (EPIDERMOID) components

HIGH YIELD ASSOCIATIONS:

• MAML2 gene rearrangement

• t(11;19)(q14-21;p12-13)

TYPICAL CLINICAL PICTURE:

• Elderly patient presents an elevated plaque on the H&N

• Most commonly arises in the parotid gland or palate

POOR PROGNOSTIC INDICATORS

• Old age

• Male

• Submandibular gland

• Extraglandular extension

• Vascular invasion (NOTE: Perineural invasion is common)

• Necrosis

• High mitotic rate

• High histologic grade

TREATMENT

• Surgical excision is 1st line of treatment. +/- radiation for local control

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KEY HISTOLOGY FINDINGS

- EXAMINE THE VIRTUAL SLIDE -

• Well-circumscribed nodules with indistinct borders- can be predominantly cystic to predominantly solid

Mucoepidermoid carcinoma- Well circumscribed (but infiltrative) deep tumor with cystic & solid components

Mucoepidermoid Carcinoma is composed of an admixture of 3 cell types:

1. Mucocytes (mucin forming cuboidal cells with bland nuclei and occasional small nucleolus- NOTE: Mucin filled microcysts & clear cell change are common with vacuolated cytoplasm)

2. Epidermoid cells (polyhedral atypical cells with dense cytoplasm)

3. Intermediate cells (mixture between the 2)

In the images below, note the cords, sheets & clusters of mucous, squamous, intermediate and clear cells.

• Background with chronic inflammation

• Deep dermal infiltration with perineural invasion is common

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GRADING MUCO-EPs (AFIP Point System)

The presence of cellular pleomorphism, mitoses, and necrosis vary with grade. There is very low concordance between pathologists, but the AFIP point system can be helpful to determine whether a MEC is low- intermediate- or high grade.

Examine the tumor and assign "points" if any of the following features are identified:

ASSIGN 2 POINTS:

• <20% intracystic component

• Neural invasion

ASSIGN 3 POINTS:

• Necrosis

• 4+ mitotic figures per 10 HPF

ASSIGN 4 POINTS:

• Anaplasia

TOTAL SCORE = 0-4 LOW GRADE

TOTAL SCORE = 5-6 INTERMEDIATE GRADE

TOTAL SCORE = 7+ HIGH GRADE

Check out some examples below; Clicking on the image or the link will open the virtual slide on PathPresenter.net.

LOW GRADE; SCORE = 0-4 (Click to view slide)

Low Grade MEC- Low grade tumors tend to be more well-circumscribed with gray-white, mucin filled cysts, bland nuclei, & form glandular spaces

INTERMEDIATE GRADE; SCORE = 5-6 (Click to view slide)

Intermediate Grade MEC- These fall somewhere in between the spectrum... not very helpful

HIGH GRADE; SCORE = 7+ (Click to view slide)

High Grade MEC- High grade tumors tend to be more solid & have an infiltrative growth pattern with <20% intracystic (mucinous) component. There are more high grade features such as atypical epidermoid & intermediate cells with cytoplasmic clearing. There are fewer mucinous cells present.

• Variants: clear cell, oncocytic cells

• Can be assocainted with tumor-associated lymphoid proliferation (TALP)

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ANCILLARY STUDIES

(EX: ADDITIONAL TESTS TO CLUE YOU IN TO THE DIAGNOSIS)

• LOW GRADE: CK7, CK14, Antimitochondrial antibodies

• Ki-67 stain & Mucicarmine could be helpful

• Electron microscopy (rarely done)- Mixed luminal epithelial cells surrounded by myoepithelial cells

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DIFFERENTIAL DIAGNOSES

• Adenosquamous carcinoma: Higher grade tumor with anaplastic features

• Metastatic or Poorly differentiated (adeno)carcinoma: Review clinical history

• Necrotizing sialometaplasia

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And there you have it...

Reference:

https://wiydx.com/DermSection/DermCase/Histological/EBA7B092-4C3B-4889-BAD5-A16B969D0A87

Handra-Luca A. Mucoepidermoid carcinoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/salivaryglandsMEC.html. Accessed July 20th, 2019.

PathPresenter.net (links provided above)