Basal Cell Carcinoma

Most common malignant skin tumour; arises from basal keratinocytes

Aetiology

• Exposure to UV radiation - the sun-exposed areas of the head and neck are the most commonly involved sites
• Sun exposure in childhood may be especially important

• Predominantly affects Caucasians - skin types I and II most at risk

• Other risk factors - immunosuppression, environmental carcinogens (e.g. smoking, ionising radiation), trauma

• Other conditions associated with an increased risk of BCC include xeroderma pigmentosa and albinism
• Xeroderma pigmentosum: defective nucleotide excision repair
• Oculocutaneous albinism: autosomal recessive absence/defect of tyrosinase resulting in absence of melanin

Pathophysiology

1. Epidermal keratinocyte DNA damanged by solar UV radiation

2. Mutation of tumour suppressor genes and loss of apoptotic function

3. Mutation of protooncogenes

4. Clonal selection of non-apoptosing, mutated cells

5. Solar UV suppresses normal cell mediated immune response agaisnt tumour cells

6. Further growth to macroscopic tumour

Growth and spread

• Slow growing, locally destructive

• Almost never mestastesizes

• Can kill by invasion e.g. eye → brain

Clinical presentation

Types of basal cell carcinoma

• Slow-growing, shiny, pearly nodule with superficial telangiectasia

• Commonly on the face

• May be ulcerated ('rodent ulcer')

• Erythematous well-demarcated scaly plaques, often larger than 20 mm at presentation

• Slightly raised 'whipcord' margin

• Slow growth over months or years

• Characterised by thickened yellowish plaques

• May infiltrate tissues widely; may spread along nerves

• Margins poorly defined

• Brown, blue or greyish lesion

• Nodular or superficial histology

• Seen more often in individuals with dark skin

• May resemble malignant melanoma

Investigations

Histopathology (Gold Standard)

• Nests of basaloid cells

• Peripheral palisading

• Clefting artifact between tumor and stroma

• Mucinous stromal retraction

Dermoscopy

• Arborizing vessels

• Blue-gray globules

• Leaf-like structures

Management

• Treatment of choice for most BCCs is a wide excision with histology to ensure complete removal of the tumour with adequate margins
• Mohs micrographic surgery is preferred for infiltrative BCCs and tumours involving the nasal creases, as these are more likely to recur

• Superficial BCCs can be managed with non-surgical treatment, including cryotherapy, photodynamic therapy and topical imiquimod

• Targeted treatment for advanced cancers/patients unable to tolerate surgery e.g. vismodegib - Hedgehog inhibitor that binds to SMO