Mucoepidermoid Carcinoma: Malignant Tumours of Salivary Glands

Definition:
It is a malignant epithelial tumour, composed of both mucous secreting cells and epidermoid type cells in varying proportions.

Note:
- Most common malignant neoplasm in salivary glands

Risk factors: 
- Ionizing radiation

Clinical features:
Age: 3rd to 5th decade (Avg: 47 years), but any age, M = F
Site: Parotid gland (most common), Buccal mucosa, tongue, retromolar area
a) Low grade malignancy:
- Slowly enlarging painless mass
- Stimulates pleomorphic adenoma
Note: Unlike pleomorphic adenoma, it shows:
   1. > 5 cm in diameter
   2. Not completely encapsulated
   3. Often contain cysts
b) high grade malignancy:
- Grows repeatedly, pain → early symptom
- facial nerve paralysis → frequently
- Trismus, drainage from ear, dysphagia and numbness adjacent area
- Ulceration (in case of minor salivary gland)
- Metastasis in lymph nodes, lung, bone, brain etc.

Histologic features:
It is composed of mucous secreting cells, epidermoid type (squamous) cells and intermediate cells and also clear cells.

- Mucous cells: Various shapes, abundant pale cytoplasm, +ve for mucin stains

- Epidermoid cells: Squamous or polygonal shapes, rare keratinization

- Intermediate cells: Larger than basal cells and smaller than squamous cells

- Clear cells: Mucin and glycogen free

Grading of Mucoepidermoid Carcinoma

1) Low grade tumours:
   - Well  formed glandular epithelium
   - Prominent cystic spaces (mucin filled)
   - Minimal cellular atypia
   - High proportion of mucous cells

2) Intermediate grade tumours:
   - Have solid areas of epidermoid cells with intermediate basal cells
   - Cyst formation is less prominent
   - All cells present but intermediate cells predominantly

3) High grade tumours:
   - cells present as solid nests or cord (epidermoid or basal)
   - Pleomorphism and mitotic activity is prominent
   - Cyst/ gland: rare
   - Necrosis and perinuclear invasion is present

Variants of Mucoepidermoid Carcinoma
1. Sclerosing mucoepidermoid carcinoma
2. Intraosseous mucoepidermoid carcinoma

Treatment:
- Surgical excision
- Radical neck dissection
- Irradiation
- Chemotherapy

Prognosis:
- High grade tumour: Poor
- Low grade tumour: Good

MCQS

1. Most common malignant neoplasm in salivary glands is
   a. Adenoid cystic carcinoma
   b.Mucoepidermoid carcinoma
   c. Adenocarcinoma
   d. Acinic cell carcinoma
Correct answer is b.

2. Tumour composed of both mucous secreting cells and epidermoid type cells is
   a. Pleomorphic adenoma
   b. Warthin's tumour
   c.Mucoepidermoid carcinoma
   d. Acinic cell carcinoma
Correct answer is a.

3. Age of onset of mucoepidermoid carcinoma is
   a: 1st decade
   b. 2nt to 3rd decade
   c. 3th to 5th decade
   d.  5th to 7th decade
Correct answer is c.

4. 5. Most common site for mucoepidermoid carcinoma is
   a. Parotid gland
   b. Submandibular gland
   c. Sublingual gland
   d. Minor salivary glands
Correct answer is a.

5. Unlike pleomorphic adenoma, mucoepidermoid carcinoma shows:

   a. > 5 cm in diameter
   b. Not completely encapsulated
   c. Often contain cysts
   d. All of the above

6. Cyst formation is prominent in which grade of mucoepidermoid carcinoma
   a. Low grade
   b. Intermediate grade
   c. High grade
   d. None of the above
Correct answer is a.

7. Poor prognosis is found in
   a. Low grade
   b. Intermediate grade
   c. High grade
   d. None of the above
Correct answer is c.