Common cancers

Sadly, from time to time, rabbits can be affected by cancer, which can take many different forms. Some cancers are more common than others and this factsheet will aim to look at those types more commonly seen in pet rabbits.

Cancer is a general term used for a class of diseases in which abnormal cells divide without control and are able to invade other tissues. Cancer cells can spread to other parts of the body through the blood and lymph systems destroying other healthy tissues in a process called metastasis.

There are many types of cancers, some more common than others. Most cancers are named after the organ in which they originate or type of cell that is initially affected. When the damaged cells start dividing abnormally, they can form lumps or masses called tumors which can then interfere with the function of organs, or they can release substances, eg hormones, that can alter the way the body functions.

Symptoms related to cancer can be quite variable depending on where the cancer is located, if and where it has spread, and how big it is.

The main categories of cancer are:

• Adenoma – usually arise from glandular tissues.
• Carcinoma – begins in the skin or in tissues that line or cover internal organs.
• Sarcoma – begins in bone, cartilage, fat, muscle, blood vessels or other connective or supportive tissue.
• Leukemia – starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the bloodstream.
• Lymphoma and myeloma – begin in the cells of the immune system (white blood cells).
• Central nervous system cancers – begin in the tissues of the brain and spinal cord.

Uterine adenocarcinoma

This is undoubtedly the most common tumor seen in female rabbits and is reported to affect up to 80% of unspayed female rabbits by the age of five.

Some breeds, including Dutch, Dwarf lop, English, Netherland Dwarfs, Tan, French Silver, Havana, and Polish rabbits seem to be more predisposed to uterine cancer, but rabbits of all breeds could be affected. There is no evidence to suggest that does who have had litters in the past are any less likely to be affected.

Affected rabbits may show clinical symptoms of reproductive failure such as abortion or still-born young. As the disease progresses the doe may become anorexic, depressed, lethargic and begin to lose weight. Blood in the urine (hematuria) may develop as well as bloody vaginal discharge. Once cancer has advanced, secondary tumors in the lungs may develop leading to problems breathing (dyspnea).

Cancer can be a prolonged disease that lasts for months to years as the tumor is normally slow growing, so owners may not notice anything wrong until the disease has reached an advanced stage.

Mammary carcinomas and adenocarcinomas

Mammary tumors are common in unspayed adult female rabbits. While some can be benign (not likely to spread), others can be very deadly.

The clinical symptoms of mammary tumors include the development of irregular-sized nipples, mammary swellings, abnormal discharge from the nipples, and open wounds. These tumors are not normally painful, although secondary infection can sometimes be seen.

Testicular neoplasia

Although reported in rabbits, testicular tumors are rare in rabbits.

Signs of disease include enlargement of one or both testicle(s). Reproductive failure may be seen in breeding bucks. There is the potential for secondary metastatic spread of these tumors to other organs, especially the lungs, with breathing problems becoming apparent if this is the case.

Clinical signs of cancer vary depending on the location and may be very indicative in some cases. Uterine adenocarcinomas are often suspected by your veterinarian detecting a lump in the caudal abdomen. Imaging techniques such as radiographs (x-rays) or ultrasound can then be used to detect the mass in the abdomen. Advanced imaging, such as computed tomography or magnetic resonance imaging scans are also diagnostic, although rarely used due to high cost.

Diagnosis of mammary carcinomas and adenocarcinomas can be made by obtaining a small sample of the cells from the mass(es) by inserting a needle and collecting some of the cells and looking at them under a microscope. Confirmation of the diagnosis can only be obtained by removing the tumor and sending samples to a specialized laboratory to perform a histopathological examination.

If detected in time, most types of cancer can be treated with surgery. Before embarking on treatment of cancer, a full clinical workup should be carried out, including radiographs of the chest, to ensure no spread of the disease has already occurred. Once the tumors have been fully removed, chest radiographs should be repeated 3-6 months after surgery to check the cancer hasn’t spread to other organs.

Ovariohysterectomy (spaying) is advised for all female rabbits at an early age to prevent uterine neoplasia from developing. Spaying is also usually the best treatment option in cases where a tumor is already present, as long as secondary tumors have not become established within the lungs or other areas of the body. If the cancer has spread, the prognosis is very poor. Chemotherapy has not shown long term success in most cases for rabbits; in severe cases, the kindest thing for your rabbit is to have them euthanised so they are not subjected to unnecessary pain and suffering.

When mammary carcinomas and adenocarcinomas are involved, a partial or complete mastectomy (surgical removal of all mammary gland tissue) and spaying is the treatment of choice. Benign tumors may not require treatment but are often removed due to the size to which they can grow. If the neoplastic tumors have spread into bone marrow, the lungs or lymph nodes, this carries a very poor prognosis and surgical intervention will not cure the disease.

Castration is the treatment of choice for testicular neoplasia; if there is no spread of the disease into the lungs then this should be curative of the disease. As with other primary tumors, if there is a spread into the lungs then treatment is often futile, and euthanasia is in the best interests of the rabbit. To prevent the disease, castration of all non-breeding male rabbits is advised.

Other types of tumors that have been reported in rabbits include:

• Papilloma: benign wart-like growths which can have a cauliflower appearance and can sometimes bleed. Papillomas that develop in the mouth are considered non-cancerous.
• Basal cell carcinoma: a type of skin cancer which can be benign or malignant and looks like a reddened patch of skin. They are often slow growing and appear over a period of time. Although they can spread locally, they rarely metastasize and spread to other parts of the body.
• Osteosarcoma: tumors that affect the bone and are considered rare in rabbits. Clinical symptoms may include lameness and hard swellings on the legs.
• Lymphoma: cancer of the lymphatic system.
• Thymoma: these tumors are found less frequently in rabbits. The only clinical symptom might be protrusion of the eyes from the globe. These cases are usually complicated because the eye is secondarily involved, but the primary cause might be somewhere else. A thymoma may, in fact, be slowly growing in the chest, compressing the vessels that transport blood to the head resulting in this particular clinical symptom.

The key to eliminating the most common types of cancers seen in rabbits is to get them neutered at a young age, as most cancers seen in rabbits are those affecting the reproductive systems.

Of course, your rabbit may be affected by other types of cancer, but treatments are constantly advancing, so always be advised by your veterinarian.