Learning Objective
Describe the epidemiology, risk factors, precursor lesions, clinical features, histopathology, variants, and prognosis of cutaneous squamous cell carcinoma.
Squamous Cell Carcinoma
Squamous cell carcinoma (SCC) is a malignant tumor of keratinocytes and is the second most common skin cancer after basal cell carcinoma.
Peak incidence occurs around age 60, especially in individuals with significant cumulative sun exposure.
Epidemiology & Risk Factors
| Risk Factor |
Mechanism / Explanation |
| Chronic UVB exposure |
DNA damage → pyrimidine dimers → mutations |
| Fair complexion |
Low melanin protection |
| Chronic ulcers/sinus tracts |
Marjolin ulcer – malignant transformation of chronic wounds |
| Hydrocarbon, arsenic exposure |
Chemical carcinogens |
| Burn scars, radiation exposure |
Chronic DNA injury |
| Immunosuppression (transplant pts.) |
Reduced immune surveillance |
| Xeroderma pigmentosum |
DNA repair defect → extreme UV sensitivity |
Common Mutations
- TP53 mutations
- HRAS mutations
Activity
Precursor Lesions
| Precursor |
Description |
| Actinic keratosis |
Sun-induced dysplasia of keratinocytes; rough, red, scaly papules on face, forearms, hands |
| Bowen disease |
SCC in situ; full-thickness epidermal dysplasia without dermal invasion |
Clinical Features
Typical Presentation
- Occurs on sun-exposed areas: face, ear, lower lip, hands, scalp
- Tan or pink nodular mass
- Ulceration is common
- May show a hyperkeratotic surface
Keratoacanthoma Variant
A well-differentiated SCC that:
- Grows rapidly (weeks)
- Forms a dome-shaped nodule with a central keratin-filled crater
- It is often self-limited and can regress spontaneously
Histopathology
| Feature |
Explanation |
| Nests of atypical keratinocytes |
Invasion into the dermis |
| Keratin pearls |
Concentric keratinization within tumor nests |
| Intercellular bridges |
Prominent desmosomes → typical of SCC |
| Variable differentiation |
Well → poorly differentiated forms |
Activity
Behavior and Prognosis
- Cutaneous SCC rarely metastasizes (except in high-risk sites: lip, ear, scars).
- Prognosis is generally excellent with complete surgical excision.
- Mohs surgery may be used in high-risk or cosmetically sensitive regions.
High-Yield Summary Table
| Aspect |
Key Points |
| Cell of origin |
Keratinocytes |
| Main risk factor |
Chronic UVB exposure |
| Precursors |
Actinic keratosis, Bowen disease |
| Clinical lesion |
Ulcerated, tan/pink nodular mass |
| Histology |
Invasive nests, keratin pearls, and intercellular bridges |
| Variant |
Keratoacanthoma (rapid growth, crater) |
| Metastasis |
Rare |
| Treatment |
Complete excision (curative) |
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