Skin cancer / tumors

A variety of skin cancers and tumors are reported in rabbits, with some occurring more commonly than others.

The following skin cancers and tumors have been reported in rabbits, with varying frequency:

• Trichoblastoma: benign skin tumors commonly seen in cats, dogs and guinea pigs, and are the most commonly seen skin tumor in rabbits. Most commonly seen on the head, neck, flanks and hind limbs, and look like raised masses on or under the dermal layer of the skin.
• Squamous cell carcinoma: aggressive skin tumors which form on the middle and outer layers of the skin. A common cause of over-exposure to ultraviolet sunlight. White rabbits, like cats, are more prone to this type of cancer and they appear as angry, reddened masses, which can ulcerate and bleed.
• Cutaneous lymphoma: often seen in pet rabbits in Europe but not so often in rabbits in America. They appear as discrete dark, raised, nodular cutaneous masses around the mouth and on the face.
• Oral papillomatosis: wart-like growths occur on the tongue and cheeks inside the mouth. They often cause no clinical signs and treatment is not required unless they start to cause the rabbit problems eating.
• Sebaceous adenitis: affected rabbits have non-pruritic (not itchy), scaly, flaky skin. The affected areas begin around the face and neck before progressing further down the body.
• Papilloma fibroma (Shope fibroma): also known as fibromatosis. Caused by the Shope fibroma virus, a naturally occurring leporipoxvirus. It leads to small flat skin tumors (warts) often found on cottontail rabbits. They often disappear over time and treatment, or surgical removal isn’t usually needed. In some cases, the warts can grow very large and affect surrounding tissues and muscles. In immunocompromised rabbits they can progress and become fatal.
• Papillomatosis: caused by the Cottontail Rabbit Papilloma Virus (CRPV). It leads to solid, horn-like growths around the eyelids and ears. The growths are often removed surgically as they can turn into squamous cell carcinomas.
• Rare neoplasias: sebaceous gland carcinoma, basal cell carcinoma, malignant melanoma (another type of skin cancer), leiomyoma and anaplastic sarcomas.

A carcinoma forms in the tissue cells or skin that line internal body organs. A sarcoma grows in the connective tissue cells, which includes muscles, deep skin tissues, cartilage and fat.

A benign tumor is one that is unlikely to spread or cause the rabbit health problems. A malignant tumor can spread to other areas of the body.

The word ‘neoplasia’ means an abnormal mass (tumor) which may or may not be cancerous.

To diagnose what type a tumor is, analysis of the cells is needed. This can be done using a fine needle aspirate (FNA) where some of the cells from the mass are taken into a syringe and needle, then spread over a microscope slide. A biopsy is another option, which involves taking a small sample of the mass (tissue) for analysis.

Getting a diagnosis is important as it means the correct treatment can be implemented.

Your veterinarian may also suggest blood tests and x-rays to check there is no spread of the cancer cells to other organs, especially with any malignant tumors (these are tumors that might spread to other areas of the body).

Usually surgical removal of the tumor is recommended. Depending upon the type of tumor, some require larger margins (the edge around the tumor) to be removed to ensure no cancerous cells are left behind so the likelihood of reoccurrence, either locally (in the same area) or in other areas of the body, is reduced.

Sebaceous adenitis is a little different and treatment with immune-suppressive medications is the treatment of choice. This is not without risk, as many rabbits carry undetected diseases such as E. cuniculi or pasteurellosis, and when the immune system is compromised, clinical signs of these other diseases can appear. This will need to form part of the conversation you have with your veterinarian.

If the tumor is removed successfully and it has not spread locally or elsewhere in the body, then treatment should be curative. There is always the chance that further tumors can appear at a later date, so checking the whole rabbit for any masses on a weekly basis is encouraged.

Natural sunlight is good for all of us. It aids the uptake of vitamin D, and rabbits are no different. However, rabbits do not cope with the heat; being fully furred they struggle to lose heat if they get too hot. It is very important that rabbits have constant shade, even on days when it is not very hot. Being outdoors in the daylight and sunshine is encouraged, for all rabbits, including house rabbits, but they should not be allowed to sunbathe nor be in direct sunlight.

The use of sun cream on the ears is generally discouraged, as rabbits will groom it off and ingestion can be dangerous, making them ill. It is far better to ensure they stay in the shade and are safe from any sunburn and heat exhaustion.

The reason why many tumors develop is not understood. Genetics may play a part, as may other external factors like housing, diet and environment.

Tips for prevention:

• Feed your rabbit a diet high in fiber – grass and hay should be the major components of their diet. Vegetables and green foods are also important. There are also some commercial rabbit mixes that have been developed to provide pet rabbits with a high-fiber diet.
• Allow them to live in an environment that is large and fulfilling.
• Provide them with a suitable companion.
• Check your rabbit regularly for any lumps or masses and get these checked out as soon as they are noticed.
• The sooner a lump is noticed, the quicker a diagnosis and treatment plan can be discussed with your veterinarian.