Summary

Cutaneous Squamous Cell Carcinoma (cSCC) is a malignant tumour of keratinocytes arising from the epidermis. It is the second most common skin cancer (after Basal Cell Carcinoma). Unlike BCC, cSCC has metastatic potential (~2-5% overall; higher in high-risk tumours). It typically presents as an indurated, scaly nodule or plaque, often with ulceration or crusting, occurring on sun-exposed skin in older individuals. Key risk factors include cumulative UV exposure, immunosuppression (especially organ transplant recipients who have 65-250x risk), and pre-existing Actinic Keratosis or Bowen's Disease (SCC in situ). Treatment is primarily surgical excision with appropriate margins (4-6mm for low-risk; wider/Mohs for high-risk). Lymph node assessment is essential for high-risk tumours. Prognosis is generally excellent for low-risk cSCC but worse for high-risk features (Size >2cm, Depth >6mm, Perineural invasion, Poor differentiation, Immunosuppression, Ear/Lip location). [1,2]

Clinical Pearls

SCC CAN Metastasise: Unlike BCC, SCC has metastatic potential (Regional lymph nodes → Distant). Don't underestimate it.

"Transplant SCC" is Aggressive: Immunosuppressed patients (especially renal transplant) have hugely increased risk (~100x) and more aggressive disease. Dermatology surveillance is essential.

Actinic Keratosis → Bowen's → Invasive SCC: This is the progression pathway. Treat precursor lesions.

High-Risk Features: Size >2cm, Depth >6mm, Perineural invasion, Poor differentiation, Ear/Lip location, Immunosuppressed host.

1. Marjolin's Ulcer (Strategies & Traps)

• Definition: SCC arising in a chronic wound, burn scar, or sinus tract.
• Latency: Average 30 years after injury.
• Aggression: Highly aggressive. Metastasis rate ~30% (vs 2-5% for standard SCC).
• Management: Wide excision (often 2-3cm margin). High index of suspicion for nodes.
• Trap: A non-healing venous leg ulcer might be a Marjolin's. BIOPSY chronic ulcers!

2. Keratoacanthoma (KA) - The Great Mimic

• Appearance: Rapidly growing (weeks). "Volcano-like" nodule with a central keratin core.
• Behaviour: Can spontaneously involute (disappear) after 3-6 months.
• Debate: Is it a benign entity or a well-differentiated SCC?
• Practice: Treat as SCC. Excision is safer than waiting.
  • Pathology Trap: A partial biopsy might just show keratin (benign) and miss the invasive edge. Excision biopsy preferred.

3. Verrucous Carcinoma

• Subtypes: Oral florid papillomatosis (Mouth), Giant condyloma of Buschke-Löwenstein (Genital), Epithelioma cuniculatum (Foot).
• Nature: Slow growing, warty, "pushing" border rather than infiltrative. rarely metastasises.

The T-stage is critical for decision making.

• T1: <2cm.
• T2: 2cm to 4cm.
• T3: >4cm OR Minor bone erosion OR Perineural invasion OR Deep invasion (>6mm).
• T4:
  • T4a: Gross cortical bone / marrow invasion.
  • T4b: Skull base invasion / brain encasement.
• N-Stage: Complex, depends on size, number, and laterality of nodes.

Key Change in AJCC 8: Staging is separate for Eyelid vs Head & Neck. Perineural invasion upgrades T-stage significantly.

Patients with one SCC often have "Field Change" - the whole area of skin (e.g., scalp, face) is sun-damaged and sprouting multiple pre-malignant AKs and SCCs. Treating the Field (Field Therapy) reduces the risk of future SCCs.

1. Topical 5-Fluorouracil (Efudix):
   • Application: Twice daily for 4 weeks to the entire sun-damaged area (e.g., whole scalp).
   • Reaction: Causes severe inflammation, redness, and crusting ("It gets worse before it gets better").
   • Outcome: Strips away dysplastic cells. Leaves fresh skin.
2. Photodynamic Therapy (PDT):
   • Alternative for large fields.
3. Oral Retinoids (Acitretin):
   • For transplant patients with explosive SCC numbers. Chemoprophylaxis.

Landmark Trials

1. Cemiplimab (Migden et al. NEJM 2018):
   • Phase 2 trial. Response rate 47% in metastatic CSCC.
   • Revolutionised management of inoperable disease.
2. Adjuvant Radiotherapy (Trovato et al.):
   • Retrospective data supports Post-Op RT for perineural invasion or N+ disease.

(As per original - restored)

What is Squamous Cell Carcinoma?

SCC is a type of skin cancer that develops from the cells in the outer layer of the skin (keratinocytes). It usually appears as a scaly, crusty lump or sore that doesn't heal, often on sun-exposed areas like the face, ears, or hands.

Is it serious?

Most SCCs are caught early and cured with surgery. However, unlike some other skin cancers (like BCC), SCC can spread to lymph nodes or other parts of the body if left untreated or if it has certain high-risk features.

What causes it?

The main cause is cumulative sun exposure (UV damage) over many years. People who are immunosuppressed (e.g., after organ transplant) are at much higher risk.

How is it treated?

The main treatment is surgery to remove the cancer with a margin of normal skin around it. Occasionally, radiotherapy is used if surgery is not possible. For advanced cases, there are new immunotherapy treatments available.

(As per original)

Common Exam Questions

1. SCC vs BCC Difference: "Can SCC metastasise?"
   • Answer: Yes. SCC can metastasise (~2-5%). BCC rarely does.
2. Precursor Lesion: "What is the precursor?"
   • Answer: Actinic Keratosis -> Bowen's -> SCC.
3. High-Risk Features: "Name 3 high-risk features."
   • Answer: Size >2cm, Depth >6mm, Perineural, Poor Diff, Ear/Lip, Immunosuppression.
4. Immunosuppression: "Who is at highest risk?"
   • Answer: Renal transplant recipients.

Viva Points

• Marjolin's Ulcer: SCC in a burn scar. Aggressive.
• Keratoacanthoma: Rapid growth "volcano". Treat as SCC.