Malignant Salivary Gland Tumors

🧬 Malignant Salivary Gland Tumors

Malignant salivary gland tumors are uncommon head and neck malignancies with diverse histology, variable clinical behavior, and complex management strategies.

Understanding their risk factors, histogenesis, clinical presentation, staging, classification, investigations, and treatment is essential for ENT examinations and clinical practice.

📌 Incidence & Epidemiology of Malignant Salivary Gland Tumors

• Incidence: ~0.5 per 1 lakh population per year

• Account for < 5% of all head and neck cancers

• Less common than benign salivary gland tumors

• Incidence increases after the 5th decade of life

⚠️ Risk Factors for Malignant Salivary Gland Tumors

1️⃣ Radiation Exposure (Most Important)

• Atomic bomb survivors
  • Increased risk of mucoepidermoid carcinoma
• Therapeutic head & neck radiation
  • Especially childhood cancers

What is the usual latent period between radiation exposure and development of Malignant Salivary Gland Tumors?

2️⃣ Occupational Exposure

Increased risk with exposure to:

• Rubber
• Nickel
• Asbestos
• Silica dust
• Plumbing, woodworking, mining industries

📌 Livestock feed processing

• Exposure to mycotoxins (produced by Aspergillus)
• Highly carcinogenic

3️⃣ Viral Associations (Not conclusively proven)

• Epstein–Barr virus (EBV) → Undifferentiated parotid carcinoma

• Cytomegalovirus (CMV) → Mucoepidermoid carcinoma

4️⃣ Nutritional Factors

• Inverse relationship with diet rich in polyunsaturated fatty acids

• Higher PUFA intake → lower salivary gland cancer risk

5️⃣ Genetic & Molecular Alterations

• Mucoepidermoid carcinoma
  → CRTC1–MAML2 gene fusion

• Adenoid cystic carcinoma
  → MYB–NFIB gene fusion

🧠 Histogenesis of Malignant Salivary Gland Tumors

🔹 1. Multicellular Theory (Older)

Each tumor arises from a specific mature cell type of the salivary gland.

➡️ Multiple cells of origin → multicellular theory

🔹 2. Reserve Cell (Stem Cell) Theory (Most Accepted)

• All tumors arise from a single undifferentiated pluripotent reserve cell

• Normal salivary gland & tumors arise via differentiation

• Earlier differentiation error → higher grade malignancy

➡️ Reserve Cell Theory explains wide histological diversity

What is the risk (%) of malignancy in Parotid, submandibular, sublingual and Minor salivary glands?

📌 Smaller the gland → higher the malignancy risk

🩺 Clinical Features of Malignant Salivary Gland Tumors

🔹 Parotid Gland

• Painless pre-/infra-auricular swelling

• Deep lobe tumors → soft palate / oropharyngeal bulge

• Accessory parotid tumors: ~1%

What is the most common site of origin of malignant salivary gland tumor in Parotid?

What are the Features Suggestive of Malignancy in a parotid malignancy?

🔹 Submandibular Gland

• Slow-growing painless swelling in submandibular triangle

• May distort floor of mouth

• Pain (30%), cervical nodes (25%)

What are the common nerves involved in malignant salivary gland tumor in Submandibular Gland?

🔹 Minor Salivary Glands

• Can arise anywhere

• Painless submucosal swelling

• Central ulceration

• Ill-fitting dentures (important clue)

• Pain / paresthesia (~25%)

What is the most common site of origin of malignant salivary gland tumor in Minor Salivary Glands?

🧪 TNM Staging (Salivary Gland Tumors)

T Staging

• T1: ≤ 2 cm, no extraparenchymal extension

• T2: > 2–4 cm, no extraparenchymal extension

• T3: > 4–6 cm and/or extraparenchymal extension

• T4a: Tumor invades Skin, mandible, ear canal, and/or facial nerve

• T4b: Tumor invades Skull base, and/or pterygoid plates, and/or encases carotid artery

N Staging

• N1: Single ipsilateral node ≤ 3 cm, no extranodal extension

• N2a: Single ipsilateral node > 3–6 cm, no extranodal extension

• N2b: Multiple ipsilateral < 6 cm

• N2c: Bilateral/contralateral < 6 cm

• N3a: > 6 cm, no extranodal extension

• N3b: Any node with extranodal extension

M Staging

• M0: No distant metastasis

• M1: Distant metastasis

🧬 Classification of Malignant Salivary Gland Tumors

22 malignant salivary gland tumor types, common ones include:

• Mucoepidermoid carcinoma
• Adenoid cystic carcinoma
• Acinic cell carcinoma
• Polymorphous adenocarcinoma (formerly PLGA)
• Salivary duct carcinoma
• Myoepithelial carcinoma
• Carcinoma ex-pleomorphic adenoma
• Squamous cell carcinoma
• Neuroendocrine carcinomas
• Lymphoepithelial carcinoma
• Sialoblastoma

🔸 Acinic Cell Carcinoma

• Low-grade tumor (~3%)

• 90% parotid

• Female predominance

• Encapsulated, solid/microcystic patterns

• Rare facial nerve or nodal involvement

🔸 Polymorphous Adenocarcinoma

• Minor salivary glands (palate)

• Low-grade, indolent

• Late recurrence (10–15 years)

• Mimics pleomorphic adenoma & adenoid cystic carcinoma

🔸 Adenocarcinoma (NOS)

• Aggressive

• Perineural invasion

• Facial nerve involvement (~20%)

• Poor prognosis

🔸 Carcinoma ex-Pleomorphic Adenoma

• Malignancy in pre-existing pleomorphic adenoma

• Risk increases with duration

• Poor prognosis

🔍 Investigations of Malignant Salivary Gland Tumors

A. Imaging

• Ultrasound: First line + FNAC guidance

• CECT: Large tumors, nerve involvement, nodes

• MRI: Best soft-tissue delineation, perineural spread

• PET-CT: Staging (false positives in Warthin’s & pleomorphic adenoma)

B. Cytology

• FNAC – initial test

• Core biopsy – if FNAC inconclusive

🛠️ Treatment of Malignant Salivary Gland Tumors

🔹 Surgery (Mainstay)

A. Parotid

• Superficial parotidectomy
• Total / Radical parotidectomy

What are the indications of Superficial parotidectomy & Total / Radical parotidectomy in Malignant Parotid Tumors?

What are the indications of Facial nerve resection in Malignant Parotid Tumors?

B. Submandibular Gland

• Early, N0 → Gland excision + Level I

• Advanced → Levels I–III or comprehensive neck dissection

C. Sublingual & Minor Salivary Glands

• Wide local excision

• N-block resection for large tumors

• Elective neck dissection often indicated

🔹 Neck Management

• Clinically N+ → Modified radical neck dissection

• Pathologically N+ → Adjuvant radiotherapy

• Clinically N0 → Elective neck treatment if high-risk

☢️ Adjuvant Radiotherapy in Malignant Salivary Gland Tumors

Indications:

• T3–T4 tumors
• High-grade histology
• Perineural / vascular invasion
• Positive margins
• Multiple nodes

💊 Chemotherapy in Malignant Salivary Gland Tumors

• Limited role

• Palliative

• Best response in adenocarcinoma NOS

• Drugs: Cisplatin, Doxorubicin, Cyclophosphamide

📌 Exam Pearls

• Smaller gland → higher malignancy risk
• Facial nerve palsy = malignancy until proven otherwise
• MRI best for perineural spread
• Surgery is the cornerstone of treatment
• Radiotherapy is adjuvant, chemotherapy mostly palliative