What is the TNM (Tumor, Node, Metastasis) staging system for cutaneous squamous cell carcinoma?

TNM Staging System for Cutaneous Squamous Cell Carcinoma

The AJCC 8th edition TNM staging system is the current standard for cutaneous squamous cell carcinoma of the head and neck, though it has significant limitations in prognostic accuracy compared to alternative systems like the Brigham and Women's Hospital (BWH) classification. 1

Current AJCC 8th Edition TNM System

Primary Tumor (T) Classification

• The T classification is based on tumor size and high-risk features, with a critical threshold of 2 cm (reduced from 5 cm in the 7th edition) 1, 2
• T1: Tumor ≤2 cm with fewer than 2 high-risk features 1
• T2: Tumor >2 cm but ≤4 cm, OR any tumor with 2 or more high-risk features 1
• T3: Tumor >4 cm or with minor bone erosion, perineural invasion of named nerves, or deep invasion (beyond subcutaneous fat or >6 mm depth) 1
• T4: Tumor with gross cortical bone/marrow invasion, skull base invasion, or skull base foramen involvement 1

High-Risk Features Defined by AJCC

• Depth >2 mm or Clark level ≥IV 1, 2
• Perineural invasion 1, 2
• Primary site on ear or non-hair-bearing lip 1
• Poorly differentiated or undifferentiated histology 1

Regional Lymph Node (N) Classification

• N0: No regional lymph node metastasis 1
• N1: Single ipsilateral lymph node ≤3 cm without extranodal extension (ENE) 1
• N2a: Single ipsilateral node ≤3 cm with ENE, OR single ipsilateral node >3 cm but ≤6 cm without ENE 1
• N2b: Multiple ipsilateral nodes ≤6 cm without ENE 1
• N2c: Bilateral or contralateral nodes ≤6 cm without ENE 1
• N3a: Any node >6 cm without ENE 1
• N3b: Any node with ENE 1, 3

Distant Metastasis (M) Classification

• M0: No distant metastasis 1
• M1: Distant metastasis present 1

Critical Limitations of AJCC 8th Edition

Poor Prognostic Discrimination

• The incorporation of extranodal extension (ENE) results in 77% of patients with nodal metastases being upstaged to N3b, and 88% classified as stage IV, which severely limits prognostic stratification 3
• AJCC 8th edition performs worse than the 7th edition in predicting disease-specific survival and overall survival for patients with metastatic disease 3

Alternative BWH Staging System

• The BWH system provides superior prognostication for localized cutaneous SCC compared to AJCC staging 1, 4
• BWH T1: Tumor with 0 risk factors 1
• BWH T2a: Tumor with 1 risk factor 1
• BWH T2b: Tumor with 2-3 risk factors 1
• BWH T3: Tumor with ≥4 risk factors OR bone invasion 1

BWH Risk Factors Include:

• Tumor diameter ≥2 cm 1
• Poorly differentiated histology 1
• Perineural invasion ≥0.1 mm 1
• Tumor invasion beyond subcutaneous fat 1

Staging Workup Requirements

Clinical Examination

• Thorough examination of regional lymph node basins is mandatory for all patients 1
• Physical examination should specifically assess for parotid and cervical lymphadenopathy in head and neck cutaneous SCC 5, 6

Imaging Considerations

• Imaging for nodal metastasis (CT, PET/CT, or ultrasound) should be considered for high-risk tumors (BWH category ≥T2b) 1
• Imaging may assess for deep structural involvement in extensive localized disease 1
• Routine staging imaging is rarely indicated given the overall low risk of nodal and distant metastases 1

Sentinel Lymph Node Biopsy

• The value of SLNB in cutaneous SCC remains unknown, though it may detect occult nodal metastases in high-risk tumors 1
• SLNB is not routinely recommended as its effect on management and outcomes is unproven 1

Special Considerations for Metastatic Disease

Parotid and Neck Involvement

• Patients with both parotid and neck node involvement have significantly worse survival (61% at 5 years) compared to parotid disease alone (79%) 6
• Advanced neck disease (N2: multiple nodes or nodes >3 cm) carries significantly worse prognosis than single positive nodes 5, 6
• Pathologic neck involvement occurs in 32% of patients with parotid metastases, even when clinically node-negative 6

Prognostic Factors

• Five-year disease-specific survival for metastatic cutaneous SCC is approximately 74% 6
• Advanced P stage (parotid involvement) and positive surgical margins independently predict worse outcomes 5, 6
• The highest percentage of local recurrence and regional metastasis occurs in BWH T2b tumors 4

Practical Application

For Localized Disease

• Use NCCN risk stratification (low-risk vs high-risk) for treatment planning, as it provides more practical clinical guidance than AJCC staging alone 1
• Consider BWH staging for more accurate prognostication in localized disease 1, 4

For Metastatic Disease

• Separate parotid (P) and neck (N) disease staging provides better prognostic discrimination than combined nodal staging 5, 6
• Document ENE status, as its presence dramatically worsens prognosis, though this results in most patients being classified as stage IV 3