Cutaneous Squamous Cell Carcinoma
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Direct answer
Cutaneous squamous cell carcinoma is a malignant proliferation of epidermal keratinocytes, most often on chronically sun-exposed skin, usually arising from actinic keratosis or Bowen disease. Its main prognostic determinants are high-risk features such as depth, poor differentiation, perineural invasion and a site on the lip or ear. Most lesions are cured by complete excision, but a minority metastasise to regional nodes, particularly when high-risk features are present.
What you must remember
- Precursors: actinic keratosis is the commonest, with Bowen disease as the in situ form; chronic scars, ulcers, sinuses and burns can also give rise to it.
- Risk factors: cumulative UV exposure, fair skin, immunosuppression including transplant recipients, arsenic, HPV infection and ionising radiation.
- High-risk features: diameter of 2 cm or more, depth of 2 mm or more, poor differentiation, perineural invasion, lip or ear site, and recurrence.
- Marjolin ulcer: squamous carcinoma arising in a long-standing ulcer, burn scar or sinus tract, with a poor prognosis and late nodal spread.
- Keratoacanthoma: a rapidly growing dome-shaped nodule with a central keratin plug that may regress spontaneously; histology is often indistinguishable from well-differentiated SCC.
- Bowen disease: SCC in situ, a well-demarcated red scaly plaque that can progress to invasive carcinoma.
- Metastasis: mainly to regional lymph nodes; distant spread is uncommon, but nodal involvement changes management.
A pathway from precursor to excision
Management begins by deciding whether the lesion is low or high risk, because that decides the margin and whether specialist referral is needed. Work through the steps in order.
- Confirm the diagnosis: take an incisional or punch biopsy, since SCC cannot be reliably separated from keratoacanthoma or other mimics on clinical grounds alone.
- Grade the histology: note differentiation and perineural invasion, because poorly differentiated tumours and nerve involvement raise the risk.
- Measure size and depth: tumours 2 cm or more across, or invading to 2 mm or more, are high risk.
- Check the site: lesions on the lip, ear and other high-risk sites merit specialist care and wider assessment.
- Examine the nodes: palpate the regional nodes, and image or biopsy them when they are suspicious.
- Choose treatment: low-risk lesions usually take wide excision with a margin of about 4 mm, while high-risk or recurrent lesions may need Mohs surgery, and radiotherapy suits patients unfit for surgery.
Where the high-risk questions trip candidates
Exam stems on squamous cell carcinoma test whether you can name the features that change prognosis.
- Trap: treating a keratoacanthoma as a benign lesion that never needs excision. Correct: it often regresses, but histology is frequently indistinguishable from SCC, so it is usually excised.
- Trap: attributing lip carcinoma risk to sunlight alone and ignoring the site. Correct: lip and ear sites are high risk for recurrence and nodal spread, which changes management.
- Trap: calling a Marjolin ulcer a simple wound complication. Correct: it is an SCC arising in a chronic ulcer or scar and needs biopsy and wide excision.
- Trap: assuming all cutaneous SCC metastasises early. Correct: most lesions are cured by excision, and metastasis is concentrated in high-risk tumours.
Frequently asked questions
Which precancerous lesion most often leads to cutaneous squamous cell carcinoma?
Actinic keratosis is the commonest precursor of cutaneous squamous cell carcinoma, and Bowen disease is its in situ form. Only a small fraction of actinic keratoses progress, but their presence signals heavy cumulative sun damage.
How does keratoacanthoma differ from squamous cell carcinoma?
Keratoacanthoma is a rapidly growing dome-shaped nodule with a central keratin plug that may regress over months. Keratoacanthoma can be histologically indistinguishable from well-differentiated squamous cell carcinoma, so most clinicians excise it.
Which features make a cutaneous squamous cell carcinoma high risk?
High-risk features include a diameter of 2 cm or more, depth of 2 mm or more, poor differentiation, perineural invasion, lip or ear location and immunosuppression. Any of these prompts wider margins, consideration of Mohs surgery and specialist review.
Where does cutaneous squamous cell carcinoma usually spread?
Cutaneous squamous cell carcinoma usually spreads first to regional lymph nodes, and distant metastasis is uncommon. Nodal disease is the main reason to assess high-risk lesions carefully and to consider nodal imaging or biopsy.
How is Bowen disease treated?
Bowen disease is treated by excision or, for large or cosmetically sensitive areas, by destructive or topical methods such as cryotherapy, imiquimod, 5-fluorouracil or photodynamic therapy. Histological clearance is more reliable than clinical clearance for an in situ squamous lesion.