Squamous cell carcinoma

Squamous cell carcinoma (SCC) is a common type of skin cancer. The squamous cell is found in the outer layers of the skin (the epidermis) and is a type of keratinocyte (a cell that makes the protein keratin).

Invasive SCC

Invasive SCC refers to cancer cells that have grown into the deeper layers of the skin (dermis).

The majority of invasive SCCs develop in solar keratoses. Solar or actinic keratoses are common small scaly lesions arising on the face, ears and hands of white skinned people who have spent many years outdoors. A thickened or tender keratosis may be developing into invasive SCC. SCCs are often crusty and may bleed easily. On the lips, SCC is more common in smokers.

SCC may also develop in thermal burn scars and longstanding leg ulcers. In genital areas, SCC are usually related to infection with papillomavirus (genital warts) or skin disease such as lichen sclerosus or lichen planus (see vulvar cancer). Oral cancer is most often due to smoking tobacco.

Invasive SCCs vary in size from a few millimetres to several centimetres in diameter. Sometimes they grow to the size of a pea or larger in a few weeks, though more commonly they grow slowly over months or years. They may be tender. Some SCCs appear as sores that fail to heal. If a sore has not healed within 3 weeks, see your doctor.

Luckily, SCC is not usually a threat to life as secondary spread (metastasis) is uncommon. SCC on the lip or ear appear to be the sites most likely to metastasise, so ulcers or lumps in these areas should be taken particularly seriously.

Squamous cell carcinoma

In situ squamous cell carcinoma

In situ SCC presents as one or more flat red scaly patches up to several centimetres wide, often found in large numbers on the lower legs. These patches are also known as ‘Bowen's disease’. ‘In situ’ means the malignant cells are confined to the epidermis, the outside layer of the skin. In situ SCC can persist as such or develop into invasive SCC (see above).

In situ SCC may be caused by:

• Sun exposure: in situ squamous cell carcinoma is most often found on sun exposed sites of fair skinned individuals. This is because ultraviolet radiation damages the skin cell nucleic acids (DNA) resulting in a mutant clone of the gene p53. This sets of uncontrolled growth of the skin cells. Ultraviolet radiation also suppresses the immune response preventing recovery from this damage.
• Immunosuppression from drugs such as ciclosporin or azathioprine. The longer the course, the more likely that skin cancer will arise, especially in sun-damaged skin.
• Human papillomavirus infection: this rarely causes in situ SCC on the skin although it does so more frequently on the genitals causing vulval and penile intraepithelial neoplasia.
• Arsenic ingestion: this characteristically results in multiple areas of in situ SCC on the trunk and limbs some years after exposure. Arsenic also causes white marks (raindrop hypopigmentation) and scaly lesions on the palms and soles (arsenical keratoses).
• Ionising radiation: in situ SCC was common on the hands of radiologists early in the 20th century.

The development of a lump or bleeding may indicate progression into invasive SCC and occurs in about 5% of lesions.

Bowen's disease

More images of squamous cell carcinoma in situ ...

Keratoacanthoma

Keratoacanthoma is an alarming lesion because it grows very quickly. It can develop into a dome-shaped nodule 2 or 3 centimetres in diameter over a few weeks! Keratoacanthomas are rarely dangerous and can even drop off by themselves. Surgical removal is usually recommended, as we cannot predict which ones will fall off and which lesions are true invasive SCCs.

Images of keratoacanthoma ...

Carcinoma cuniculatum

Carcinoma cuniculatum is a very rare type of low-grade invasive SCC. It also known as ‘verrucous carcinoma’. It is found on the sole of the foot and probably starts off as a plantar wart. It grows very slowly and has a hard horny surface.

Carcinoma cuniculatum

Metastatic SCC

Most SCCs remain localised but they can occasionally spread to other sites of the body. These secondary growths are known as metastases. Metastases usually develop in the nearest lymph glands, and are most likely if the original SCC is on the lip or ear. Secondary growths are more difficult to treat than the original skin lesion, as surgery may not always remove them completely.

About 100 New Zealanders die every year from cutaneous SCC.

Treatment

The treatment for a SCC depends upon its type, its size and location, the number to be treated, and the preference or expertise of the doctor.

• Excision The lesion is cut out and the skin is stitched up. This is the most common treatment for invasive SCC.
• Cryotherapy Dermatologists sometimes use liquid nitrogen with a special technique. This may be suitable for small or flat lesions of in situ SCC or thickened solar keratoses.
• Shave, curettage, & cautery (and other similar techniques) Many skin cancers can be successfully treated by shaving off or scraping out the lesion then cauterising the base. The wound usually heals rapidly without the need for stitches.
• More complex surgery Patients with larger lesions or one in a difficult site may be referred to a dermatologist or plastic surgeon, who may create a flap or graft to repair the defect after excision. Mohs micrographic surgery may be necessary.
• Radiotherapy (X-ray treatment) - Radiation treatment can be used for some skin cancers, usually on the face.
• 5-Fluorouracil cream This cytotoxic cream applied for several weeks often clears in situ SCC. It causes a vigorous skin reaction that may ulcerate. Sometimes the lesion recurs months or years later, when it may be treated the same way or by another method.
• Imiquimod Imiquimod is an immune response modifier in a cream base. Applied five times weekly for six to sixteen weeks, it will clear most patches of in situ SCC but is not yet registered for this purpose.
• Photodynamic therapy 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 a "burn" and then heals over a couple of weeks or so. Metvix PDT is now available to treat superficial skin cancers in New Zealand.

Whatever the chosen treatment, SCC can usually be cured. Occasionally, SCCs come back at the same site, but they can then usually be treated again effectively.

If you have had one SCC treated, you have an increased chance of developing further SCCs.

• Early detection means easier treatment, and less scarring.
• Make sure you protect your skin from the sun at all times. Use a broad spectrum sunscreen.
• Arrange for a complete skin examination from time to time.
• Ask your dermatologist or GP to check any persisting or growing lumps or sores.