Intraepidermal squamous cell carcinoma (SCC) is a common superficial form of skin cancer. It is also known as Bowen disease, intraepidermal carcinoma (IEC) and carcinoma in situ of the skin.
Intraepidermal SCC is derived from squamous cells, the flat epidermal cells that make keratin—the horny protein that makes up skin, hair and nails. ‘Intraepidermal’ and ‘in situ’ mean the malignant cells are confined to cell of origin, ie, the epidermis.
Intraepidermal SCC presents as one or more irregular scaly plaques of up to several centimetres in diameter. They are most often red but may also be pigmented.
Although intraepidermal SCC may arise on any area of skin, it is most often diagnosed on sun-exposed sites of the ears, face, hands and lower legs. When there are multiple plaques, distribution is not symmetrical (unlike psoriasis).
As intraepidermal SCC is confined to the surface of the skin, there are various ways to remove it. Recurrence rates are high, whatever method is used, particularly in immune suppressed patients.
Solitary lesions can be cut out, and the defect repaired by stitching it up. Excision is necessary if there is suspicion of invasive SCC.
Superficial skin surgery refers to shave, curettage and electrosurgery, and is a good choice for solitary or few hyperkeratotic lesions. The lesion is sliced off or scraped out, then the base is cauterised. Dressings are applied to the open wound to encourage moist wound healing over the next few weeks.
Cryotherapy means removing a lesion by freezing it, usually with liquid nitrogen. Moderately aggressive cryotherapy is suitable for multiple, small, flat patches of intraepidermal SCC. It leaves a permanent white mark at the site of treatment.
5-fluorouracil cream contains a cytotoxic agent and can be applied to multiple lesions. The cream may be applied to intraepidermal SCC for 4 weeks, and repeated if necessary. It causes a vigorous skin reaction that may ulcerate.
Imiquimod cream is an immune response modifier used off-licence to treat intraepidermal SCC. It is applied 3–5 times weekly for 4–16 weeks and causes an inflammatory reaction.
Photodynamic therapy (PDT) refers to treatment with a photosensitiser (a porphyrin chemical) that is applied to the affected area prior to exposing it to a strong source of visible light. The treated area develops an inflammatory reaction and then heals over a couple of weeks or so. The best studied, methyl levulinate cream PDT used off licence, provides high cure rates for intraepidermal SCC on the face or lower legs, with excellent cosmetic results. The main disadvantage is the pain experienced by many patients during treatment.