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Geriatric focus: Growing Lumps and Cancer
As our pets age we see an increase incidence of tumors or lumps. Although it is always wise to have these lumps examined by a veterinarian, thankfully some may be benign and therefore do not need removal.
Growths or tumours that do not spread to other parts of the body and tend not to invade other surrounding tissues - are termed 'benign' tumours. We diagnose many benign lumps/tumors in dogs including skin growths called histiocytomas and sebaceous adenomas. Many older dogs will develop a soft lump under the skin called a lipoma, which is considered benign and is composed of fatty tissue.
The term cancer is often used to describe 'malignant' tumours, which do invade surrounding normal healthy tissue, and may spread to other locations in the body (or metastasize). Cancers are known to typically spread via the blood stream or lymphatic system to other distant sites. Due to their invasive nature, malignant tumours (cancers) are generally more serious than benign tumours, often causing more serious and extensive disease.
Q: How common is cancer in older pets?
A: In pets the rate of cancer increases with age. Cancer is responsible for approximately half the deaths of pets over 10 years of age. Dogs get cancer at roughly the same rate as humans, while cats tend to have lower rates of cancer. Some cancers, such as breast or testicular cancer, are largely preventable by spaying and neutering.
Q: How is Cancer Diagnosed?
A: A diagnosis of cancer may be based on x-rays, blood tests, physical appearance of tumors, and other physical signs. Your veterinarian may be suspicious that a growth may be cancerous, but the actual diagnosis of cancer can only be made by the microscopic examination of cells/tissues generally by an experienced pathologist. This will usually necessitate a biopsy or the surgical removal of a small piece of tissue or the complete removal of the lump, an excisional biopsy, by your veterinarian. In some cases it may be possible to make a diagnosis from either a 'fine needle aspirate' (a small needle is inserted into the tumor/lump to remove or ‘suck out' a few cells that can be put on a slide for examination) or a ‘needle biopsy' (where a larger needle is inserted into a lump to remove a very small 'core' of tissue). Occasionally other techniques are also used to obtain samples of the suspected abnormal cells so that a diagnosis can be made. Blood samples are a routine part of the investigation of any suspected cancer patient, however very few pets actually show cancer cells in their blood unless it is a cancer such leukemia or occasionally mast cell tumors. Blood panels are instead performed to detect any adverse effects of the cancer, and to detect the presence of any other disease.
Q: What are the common cancers affecting cats (see website: fabcats.org/owners/cancer/info1.html)
Lymphoma -malignant lymphoma, lymphosarcoma is probably the single most common cancer that affects cats. Clinical signs vary according to the tissues that are affected. Both infection with leukaemia virus and immunodeficiency virus can be underlying or predisposing causes of lymphoma development.
Squamous cell carcinoma – This is a cancer of the skin. Exposure to sunlight is one trigger-factor for this cancer and it is seen more commonly in white cats. The tumour commonly affects the nose or the ears and can initially look like a small scratch or wound that won't heal. Spread (metastasis) of these tumours is uncommon but local lymph nodes are sometimes affected.
Early treatment of these tumours can be very successful and most commonly involves surgical removal or radiation therapy. For some tumours affecting the superficial layers of the skin local radiation therapy (applied via a probe touched onto the skin) can be very effective. The response to drug therapy (chemotherapy) is generally not very good. For some affected cats, an alternative to conventional surgery may be 'cryosurgery' where the affected tissue is frozen using liquid nitrogen applied via a special probe, although conventional surgery and/or radiation therapy are usually preferred options.