Criteria

Histopathological classification[78]

Bowen's disease (squamous cell carcinoma [SCC] in situ):

  • Full-thickness atypia that is confined to the epidermis, with an intact basement membrane.

Invasive SCC:

  • Tumour extends beyond the basement membrane, penetrates into the dermis, and may invade deeper structures.

Clinicopathological classification[79]

  • Well differentiated

  • Moderately differentiated

  • Poorly differentiated

  • Spindle cell subtype

Broders classification[80]

  • Grade 1: 75% keratinocytes are well differentiated

  • Grade 2: >50% keratinocytes are well differentiated

  • Grade 3: >25% keratinocytes are well differentiated

  • Grade 4: <25% keratinocytes are well differentiated

American Joint Committee on Cancer (AJCC) TNM staging system (8th edition)[81]

The AJCC staging system describes the extent of disease based on the following anatomic factors: size and extent of the primary tumour (T); regional lymph node involvement (N) (assessed clinically [cN] and pathologically [pN]); and presence or absence of distant metastases (M). Nonanatomic prognostic factors (e.g., tumour grade) can be used to supplement staging.

The AJCC staging system (8th edition) only includes staging for cutaneous squamous cell carcinoma of the head and neck.

Brigham and Women's Hospital tumour staging for cutaneous squamous cell carcinoma[82][83]

  • T1: 0 high-risk factors*

  • T2a: 1 high-risk factor*

  • T2b: 2-3 high-risk factors*

  • T3: ≥4 high-risk factors*

  • T4: n/a

*High-risk factors contributing to poor outcomes include tumour diameter ≥2 cm; poorly differentiated histology; tumour invasion beyond subcutaneous fat (excluding bone invasion, which automatically upgrades tumour to Brigham and Women's stage T3); perineural invasion ≥0.1 mm; and location on the ear, temple, or anogenital region.[82]

Although population-based validation is required, Brigham and Women's Hospital tumour staging outperformed American Joint Committee on Cancer (AJCC) and Union for International Cancer Control (UICC) tumour staging systems for cutaneous SCC in an analysis of 1818 primary tumours diagnosed from 2000 to 2009 at Brigham and Women's Hospital.[83]

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