Basal Cell & Squamous Cell Carcinoma

The Concept

The two common non-melanoma skin cancers — basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) — both arise from keratinocytes of the epidermis and are strongly related to cumulative ultraviolet (sun) exposure. They are far commoner and generally far less dangerous than melanoma, but they behave differently from each other, and the key distinction is their tendency to metastasise.

Basal Cell Carcinoma (rodent Ulcer)

BCC is the commonest skin cancer, arising from the basal layer of the epidermis, typically on sun-exposed skin of the face (classically above a line from the angle of the mouth to the ear). Its defining behaviour is that it is locally invasive but very rarely metastasises. The classic nodular BCC is a slow-growing 'rodent ulcer' — a pearly nodule with a rolled, beaded edge, surface telangiectasia and central ulceration. Other types are superficial and morphoeic. Treatment is surgical excision with a margin, Mohs micrographic surgery for the face or recurrent lesions, and radiotherapy or topical therapy in selected cases.

Squamous Cell Carcinoma

SCC also arises on sun-exposed skin but, unlike BCC, can metastasise (to regional lymph nodes). It frequently develops from precursor lesions — actinic (solar) keratoses and Bowen's disease (SCC in situ) — and can arise in chronic wounds, scars and sinuses (a Marjolin's ulcer). It presents as a keratotic, crusted or ulcerated nodule with an everted, raised edge. Risk is increased by sun exposure, immunosuppression and chronic inflammation. Treatment is excision with an adequate margin (or radiotherapy), with treatment of involved nodes.

BCC VS SCC

Precursor & Premalignant Lesions

An important theme with SCC is its development from recognisable premalignant lesions, which offers a chance for early treatment. Actinic (solar) keratoses are rough, scaly patches on sun-damaged skin that carry a small risk of progressing to SCC; Bowen's disease is SCC in situ — a persistent red scaly plaque confined to the epidermis. Recognising and treating these (with cryotherapy, topical agents or excision) can prevent invasive cancer, and their presence signals a field of sun-damaged skin at risk of further tumours.

The Role of Immunosuppression

A clinically important point is the marked increase in non-melanoma skin cancer — especially SCC — in immunosuppressed patients, particularly organ transplant recipients on long-term immunosuppression. In these patients SCCs are more numerous, more aggressive and more likely to metastasise. This underlines the role of immune surveillance in controlling these UV-driven cancers, and means such patients need regular skin surveillance and prompt treatment of any suspicious lesion.

Mohs Surgery & Margin Control

Mohs micrographic surgery deserves explanation as it is frequently mentioned for BCC. It involves excising the tumour in thin layers, each examined microscopically at the time until a completely clear margin is achieved. This gives the highest cure rate while sparing the maximum normal tissue, making it ideal for tumours on the face (where tissue conservation matters cosmetically), at high-risk sites, and for recurrent or morphoeic BCCs with ill-defined margins.

A Note on Prevention & Sun Protection

Because non-melanoma skin cancers (and melanoma) are so strongly driven by ultraviolet exposure, prevention is an important, examinable dimension. Advising sun avoidance at peak times, protective clothing and hats, broad-spectrum sunscreen, and avoidance of sunbeds reduces the cumulative UV damage that causes these tumours. Public education and, in high-risk individuals (fair skin, prior skin cancer, immunosuppression), regular skin surveillance for early detection complete a prevention-and-screening strategy that materially reduces skin-cancer burden.

• BCC = commonest skin cancer; 'rodent ulcer' (pearly, rolled edge, telangiectasia); locally invasive, rarely metastasises.
• SCC = can metastasise to nodes; everted edge; from actinic keratosis/Bowen's/Marjolin's ulcer.
• Both UV-related; treat by excision (Mohs for facial/recurrent BCC); treat nodes in SCC.

BCC almost never metastasises; SCC can.

• BCC and SCC = non-melanoma skin cancers from keratinocytes; UV-related; less dangerous than melanoma.
• BCC: commonest skin cancer; 'rodent ulcer' (pearly nodule, rolled/beaded edge, telangiectasia); locally invasive but rarely metastasises.
• SCC: can metastasise to lymph nodes; everted edge; arises from actinic keratosis, Bowen's disease (in situ) or Marjolin's ulcer.
• Treat both by excision with a margin (Mohs for facial/recurrent BCC; radiotherapy an option); treat involved nodes in SCC.