Rodent ulcer (basal cell carcinoma)

What is a rodent ulcer?

A rodent ulcer is a common type of skin cancer, also known by its medical name, basal cell carcinoma (BCC). It develops in the deepest layer of your skin, grows slowly, and almost never spreads beyond that area.

What are the symptoms of a rodent ulcer?

A rodent ulcer can look different from person to person, and it often grows so slowly that you may not notice it at first. Watch out for:

• a small, shiny lump with a pearl-like look, sometimes showing tiny blood vessels on the surface
• a flat, scaly patch of red or pink skin, which can resemble eczema
• a scab that bleeds and will not fully heal
• an open sore that stays present for longer than four weeks, or one that heals and then reappears
• a patch that oozes, crusts over or bleeds without an obvious cause.

Most cause no pain at all, but a few feel itchy or bleed a little if you knock them.

What causes a rodent ulcer, and who is at risk?

The main cause of a rodent ulcer is long-term exposure to ultraviolet (UV) light, whether from the sun or from sunbeds. Over many years, UV light damages the DNA inside a skin cell in the deepest layer of your skin, and that cell begins to divide and grow out of control.

You are more likely to develop a rodent ulcer if you have:

• skin that tends to burn rather than tan, especially with fair or red hair
• spent a lot of time in the sun over the years, for example through outdoor work, hobbies, or living somewhere sunny
• used sunbeds or sunbathed often
• had a rodent ulcer before
• a weakened immune system, for example after an organ transplant
• had radiotherapy in the past, particularly as a child
• long-term contact with arsenic
• a rare inherited condition called Gorlin syndrome.

Age plays a part too: rodent ulcers are most common in people over 40, although doctors are now seeing more younger people affected. Fair skin and a tendency to freckle can run in families, but a rodent ulcer itself is not usually inherited.

Are there different types of rodent ulcer?

Yes. Doctors group rodent ulcers into a few main types, based on how they look and grow:

• nodular, the most common type, usually a small, shiny lump
• superficial, a flat, scaly patch, often on the chest or back
• morphoeic, also called infiltrative, which grows into deeper layers of skin and can be harder to spot and treat
• pigmented, which contains extra colouring and so can look darker than the surrounding skin.

Nodular and superficial rodent ulcers are usually classed as lower risk, since they are less likely to return once treated. Morphoeic and infiltrative types carry a higher risk of returning, so your doctor may suggest a different treatment approach for these.

How is a rodent ulcer diagnosed?

Your doctor may be able to tell you have a rodent ulcer just by looking at it, sometimes using a hand-held magnifier called a dermatoscope for a closer look.

If there is any doubt, they will take a small skin sample, called a biopsy, under local anaesthetic, usually about 4mm across or smaller. This is sent to a specialist to be examined under a microscope, and the small hole it leaves is usually closed with a stitch or two that dissolve naturally.

The biopsy results confirm the diagnosis and the exact type of rodent ulcer, which helps your doctor plan the right treatment for you.

How is a rodent ulcer treated?

The right treatment for a rodent ulcer depends on its size, type and position, and on how many rodent ulcers you have. Some can be treated without surgery, while others need an operation.

Non-surgical treatment

For low-risk, superficial rodent ulcers, your doctor may offer treatment that does not involve cutting. Options include:

• an immune-boosting cream (imiquimod) applied five times a week for six weeks, clearing around eight in ten thin rodent ulcers
• a chemotherapy cream applied directly to the skin
• cryotherapy, which freezes the area with liquid nitrogen and leaves a small scar as it heals
• photodynamic therapy, where a light-sensitive cream is applied to the skin and then activated with red light
• curettage and cautery, where the ulcer is scraped away with a small instrument and the area is then sealed using heat.

Radiotherapy, a course of X-ray treatment, is sometimes used for larger or more advanced rodent ulcers that are not suitable for surgery. Non-surgical treatments can carry a slightly higher chance of the rodent ulcer returning than surgery does.

Surgical treatment

Surgery is the most common treatment for a rodent ulcer and usually gives the best chance of a full cure, especially for ulcers on the face, head or neck. Most operations use a local anaesthetic, so you stay awake but do not feel pain.

1. Your surgeon marks the edge of the rodent ulcer, along with a rim of healthy-looking skin around it, usually 4–5mm wide.
2. A local anaesthetic injection numbs the area before the procedure begins.
3. The rodent ulcer and the marked rim of skin are removed and sent to a laboratory for examination under a microscope.
4. The wound is closed with stitches, or occasionally a skin graft, and covered with a dressing.

For rodent ulcers that have come back after previous treatment, or that sit in tricky areas with little spare skin, your surgeon may suggest Mohs micrographic surgery. During this procedure, a thin layer of tissue is removed and examined under a microscope straight away, and further layers are only taken if cancer cells remain. This is only available at a small number of specialist centres in the UK, and you may need a separate appointment with a reconstructive surgeon afterwards.

When should I see a doctor?

See your GP if you notice:

• a spot, scab or sore that is growing, changing shape or colour, or bleeding
• a mark that has not healed within four weeks
• any new change to the skin near a rodent ulcer you have had treated before.

Checking your skin once a month, and asking someone to check hard-to-see areas like your back, helps you spot problems early. A rodent ulcer will not disappear by itself, and if it is left for a long time it can damage the skin and tissue around it. Treating it early usually means removing less tissue and gives you a better chance of a complete cure.