Squamous Cell Carcinoma

SCC Basics - Sunny Side Scourge

• Malignant tumor of epidermal keratinocytes, often showing keratinization (keratin pearls).
• Second most common skin cancer (after BCC); higher metastatic potential than BCC.
• Key Risk Factors:
  • Sun Exposure: Chronic UVB > UVA. Main cause for cutaneous SCC.
  • Immunosuppression: Organ transplant recipients (↑65-250x risk), HIV.
  • Chronic Inflammation: Scars (Marjolin's ulcer), chronic ulcers, sinuses (e.g., osteomyelitis).
  • HPV: Esp. types 16, 18 (anogenital, periungual, oral SCC).
  • Chemicals: Arsenic, tar, soot.
  • Radiation: Ionizing radiation.
  • Genetic: Xeroderma Pigmentosum (XP), Albinism, Epidermolysis Bullosa.
  • Precursors: Actinic keratosis (AK), Bowen's disease (SCC in situ), Leukoplakia.

⭐ UVB radiation (290-320 nm) is the most implicated etiological factor for cutaneous SCC, primarily through formation of pyrimidine dimers.

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Clinical Canvas - Spot the Suspect

• Presentation: Firm, indurated papules, plaques, or nodules; often scaly, crusted, ulcerated, or hyperkeratotic. Friable, bleeds easily.
  • Common sites: Sun-exposed skin (face, ears, lower lip, hands), mucous membranes.
• Key Variants:
  • SCC in situ (Bowen's Disease): Well-defined, erythematous, scaly patch/plaque. Non-invasive.
    • Genital variant: Erythroplasia of Queyrat.
  • Keratoacanthoma (KA): Rapidly growing, dome-shaped nodule with central keratin plug. "Crateriform."
  • ⭐ Marjolin's Ulcer:

    Marjolin's ulcer, an SCC arising in chronic wounds, burns, or scars (e.g., chronic osteomyelitis sinus tracts), is often more aggressive and has a higher metastatic potential.

• Symptoms: Often asymptomatic; may be tender or pruritic. Perineural invasion (PNI) can cause pain, paresthesia.

Microscopic Clues & Staging - Deep Dive Diagnosis

• Biopsy is Gold Standard: Confirms SCC.
  • Histopathology (HPE):
    • Atypical squamous cells: Invasive cords/nests.
    • Keratin pearls (📌 "Onion rings").
    • Intercellular bridges (desmosomes).
    • Cellular pleomorphism, hyperchromasia, ↑mitotic activity.
    • Grading: Well, moderately, poorly differentiated.

  ⭐ Histopathologically, SCC is characterized by invasive cords and nests of atypical squamous epithelial cells with features like keratin pearls, intercellular bridges, and varying degrees of differentiation.

• Staging (AJCC TNM 8th Ed.): Guides prognosis & treatment.
  • T (Tumor): Size & invasion depth.
    • T1: ≤ 2 cm. T2: >2-4 cm. T3: >4 cm/PNI/deep invasion. T4: Bone/skull base.
  • N (Nodes): Regional lymph node spread.
    • N1: Single ipsilateral ≤ 3 cm.
  • M (Metastasis): Distant spread.
    • M1: Present.

Treatment Tactics - Eradication Roadmap

• Risk Stratification: Guides therapy (Low vs. High-risk).
• Surgical (Primary):
  • Excision: Margins 4-6 mm (low-risk), 6-10 mm (high-risk).
  • Curettage & Electrodessication (C&E): Small, low-risk.
  • Cryosurgery: Superficial, low-risk.

  ⭐ Mohs Micrographic Surgery (MMS) is the treatment of choice for high-risk SCCs (e.g., large size, aggressive histology, recurrent, critical anatomical sites like face/ears/hands) due to its high cure rate and maximal tissue conservation.

• Non-Surgical:
  • Radiotherapy (RT): Primary or adjuvant.
  • Topical: 5-Fluorouracil (5-FU), Imiquimod (SCC in situ/Bowen's).
• Advanced/Metastatic: Systemic (Immunotherapy, Chemotherapy, EGFR inhibitors).
• Adjuvant: RT for high-risk features (PNI, +margins).
• Prevention: Sun protection, skin checks.

High‑Yield Points - ⚡ Biggest Takeaways

• Second most common skin cancer, arises from epidermal keratinocytes.
• Major risk: Chronic sun exposure (UVB). Others: immunosuppression, HPV, chronic scars (Marjolin's ulcer), arsenic.
• Precursors: Actinic keratosis, Bowen's disease (SCC in situ).
• Clinically: Indurated, scaly, crusted, or ulcerated lesion, often bleeds easily.
• Higher metastatic risk than BCC; lip/ear lesions, perineural invasion, and immunosuppression are high-risk factors.
• Diagnosis: Full-thickness biopsy. Treatment: Surgical excision; Mohs for high-risk lesions.