POTENTIALLY PRE-MALIGNANT CUTANEOUS TUMOURS:

Solar keratoses (actinic keratoses)
These frequently develop later in life in white-skinned people who have had significant sun exposure. They appear on exposed skin as erythematous silver-scaly papules or patches with a conical surface and a red base (Fig. 23.31). The background skin is often inelastic, wrinkled and may show flat brown macules ('liver spots' or solar lentigos) reflecting diffuse solar damage. A small proportion of these keratoses can transform into squamous cell carcinoma but only after many years.
Treatment of lesions is with cryotherapy, topical 5-fluorouracil cream or 5% imiquimod cream.
Bowen's disease
This is a form of intraepidermal carcinoma-in-situ which rarely can become invasive. It presents on exposed skin as an isolated scaly red patch or plaque, looking rather like psoriasis, although it has a rather irregular edge. The lesions do not clear but slowly increase in size with time.
A variant which can show partial or full-thickness dysplasia can involve the epidermis of the mucosa or neighbouring skin - this can affect the vulva, the glans penis and perianal skin. It is termed vulval- (penile-, or anal-) intraepithelial dysplasia. Clinically it can present as non-specific erythema or as a warty thickening. These diseases have a stronger link with HPV and probably have a higher premalignant potential than Bowen's disease. They are commoner in immunosuppressed individuals. The anal form is increasingly reported in HIV-positive patients and extension into the rectum has been reported.

Treatment is with topical 5-fluorouracil, 5% imiquimod cream, cryotherapy, curettage, photodynamic therapy or a tissue-destructive laser.
Atypical mole syndrome (dysplastic naevus syndrome)
This is often familial. A large number of melanocytic naevi begin to appear in childhood, even on unexposed sites. Individual lesions may be large with irregular pigmentation and border, and histologically they may show cytological and architectural atypia but no frank malignant change. Individuals with this condition have an increased risk of developing malignant melanoma. They should have their moles photographed and be regularly reviewed. Suspicious lesions should be excised.
Giant congenital melanocytic naevi
These are very large moles present at birth. They show an increased risk of developing malignant melanoma. Approximately 10% of lesions larger than 20 cm across will develop a malignant melanoma in childhood. Excision should be undertaken if possible.
Lentigo maligna
This is a slow-growing macular area of pigmentation seen in elderly people, commonly on the face. The border and pigmentation are often irregular. Some people regard this lesion as a melanoma-in-situ. There is an increased risk of developing invasive malignant melanoma. Treatment is by excision if possible but 5% imiquimod cream is currently under assessment in the very large lesions where surgery would be so disfiguring.