Canine Tumors and Cancers

Most people associate the word tumor with a growth occurring on the skin or somewhere in the body. However, any sort of lump, bump, growth or swelling (such as an abscess) is a tumor. Those which are true growths are called neoplasms.

Benign neoplasms are growths which do not invade and destroy, nor do they spread. They are cured by surgical removal.

Malignant neoplasms are the same as cancers (also called carcinomas, sarcomas, or lymphomas depending upon the cell type). Cancers invade and destroy. They tend to spread via the bloodstream and lymphatic system to distant parts of the body. This is called metastasizing.

Cancers are approached in the following manner: Suppose a female dog has a lump in her breast. Since it is solid, it is probably a neoplasm. It could be benign or malignant. The decision is made to biopsy the lump. This is a surgical operation during which the lump, or a part of the lump, is removed and sent to the pathologist who will make a diagnosis by visual inspection of tissue under microscope.

Causes

Although much has been learned, the exact cause of cancer is unknown. Long-standing irritants to tissues are a definite cause of some cancers. The irritant agent appears to speed up tissue repair (and therefore the rate of cell reduplication, or mitosis) and interferes with the immune mechanism which destroys newborn cancer cells.

Agents Known to Increase the Risk of Cancer

Examples of agents known to increase the risk of cancer in people are: ultra-violet rays (skin cancer), x-rays (thyroid cancer); nuclear radiation (leukemia); chemicals (aniline dyes causing bladder cancer); cigarettes and coal tars (causing lung and skin cancer); viruses (causing experimental cancer in laboratory animals); and parasites (a cause of bladder cancer).

Some benign tumors, such as warts and oral papillomas, are clearly due to a virus infection.

Signs of Cancer

About half the cancers occurring in dogs are visible as growths or sores on the outer surface of the body (on or beneath the skin, in the perianal area, in the mouth, and in breast tissue). Signs that a tumor can be a cancer are visible growth, ulceration of the skin with bleeding, and a sore which does not heal. One other sign is a lump or knot in a place where none should be (the breast). If you observe any of these signs, be sure to discuss them with your veterinarian.

Some tumors occur internally where you would be unlikely to detect them until they were quite large. When your dog has difficulty eating and digesting his food, or when he has an unexplained bowel disturbance, such as constipation or the passage of blood, you should consider the possibility of gastrointestinal cancer.

Cancer in the reproductive tract of females causes few signs, but you should look for vaginal discharge and bleeding.

Canine conjunctival tumors (hemangiomas and hemangiosarcomas) are also common, but under-reported. Risk of conjunctival tumors is seen more often in dogs with increased outdoor activity. Early surgical therapy is recommended and may be curative; however, recurrence is possible and more likely with hemangiosarcomas.

References:
1. Dog Owner's Home Veterinary Handbook by Delbert G. Carlson, D.V.M. and James M. Giffin, M.D.
2. Canine conjunctival hemangioma and hemangiosarcoma: a retrospective evaluation of 108 cases (1989-2004). Pirie CG, Knollinger AM, Thomas CB, Dubielzig RR. Vet Ophthalmol. 2006 'Jul-Aug;9(4)