TNM Staging System for Cutaneous Squamous Cell Carcinoma

Current AJCC 8th Edition TNM System

• The American Joint Committee on Cancer (AJCC) recommends a T classification based on tumor size and high-risk features, with a critical threshold of 2 cm, for cutaneous squamous cell carcinoma of the head and neck 1, 2
• The AJCC 8th edition defines T1 as tumor ≤2 cm with fewer than 2 high-risk features 1
• The AJCC 8th edition defines T2 as tumor >2 cm but ≤4 cm, OR any tumor with 2 or more high-risk features 1
• The AJCC 8th edition defines T3 as tumor >4 cm or with minor bone erosion, perineural invasion of named nerves, or deep invasion (beyond subcutaneous fat or >6 mm depth) 1, 2
• The AJCC 8th edition defines T4 as tumor with gross cortical bone/marrow invasion, skull base invasion, or skull base foramen involvement 1
• The AJCC 8th edition defines high-risk features as depth >2 mm or Clark level ≥IV, perineural invasion, primary site on ear or non-hair-bearing lip, and poorly differentiated or undifferentiated histology 1

Alternative BWH Staging System

• The Brigham and Women's Hospital (BWH) system provides superior prognostication for localized cutaneous SCC compared to AJCC staging 1, 2
• The BWH system defines T1 as tumor with 0 risk factors 1, 2
• The BWH system defines T2a as tumor with 1 risk factor 1, 2
• The BWH system defines T2b as tumor with 2-3 risk factors 1, 2
• The BWH system defines T3 as tumor with ≥4 risk factors OR bone invasion 1, 2
• BWH risk factors include tumor diameter ≥2 cm, poorly differentiated histology, perineural invasion ≥0.1 mm, and tumor invasion beyond subcutaneous fat 1, 2

Staging Workup Requirements

• The American Academy of Dermatology recommends thorough examination of regional lymph node basins for all patients 1
• Imaging for nodal metastasis (CT, PET/CT, or ultrasound) should be considered for high-risk tumors (BWH category ≥T2b) 1
• Routine staging imaging is rarely indicated given the overall low risk of nodal and distant metastases 1

Practical Application

• The National Comprehensive Cancer Network (NCCN) recommends using NCCN risk stratification (low-risk vs high-risk) for treatment planning, as it provides more practical clinical guidance than AJCC staging alone 1, 2
• Consider BWH staging for more accurate prognostication in localized disease 1, 2