General Information about Cancer

Cancer is an abnormal process in the body that occurs when a normal cell has been damaged and survives in a mutated form. It is generally accepted that it takes at least 2-6 spots of damaged DNA (the “code” inside each cell that determines its function) before cancer can occur. Once that damage is done, our body has many defenses against cancer and will often direct the cell to die or will kill the cell with certain parts of the immune system. If the damaged cell survives these controls and is able to divide into 2 cells, and from 2 cells to 4, etc., then cancer may occur.

Cancer can be in a solid form, which is commonly called a tumor, or in a blood-bourne form, as in leukemia. As cancer continues to proliferate beyond the control of the rest of the body, it begins to interfere with the normal functions of the body. This causes clinical signs. Sometimes a cancer cell creates a signal that disrupts normal body processes distant from the tumor itself. This is called a paraneoplastic syndrome and may include alterations in blood calcium, sugar, or hormones. The excess or lack of these substances can also cause clinical signs.

Some cancers are better than others at metastasis. This is when a cell from the tumor moves into the circulation (either blood or lymph channels) and is carried to another part of the body. If that tumor cell successfully arrives at a distant site and is able to invade the tissues at this new site and again divide into 2 cells, and 2 into 4, etc., then a metastasis has formed. The most common site of metastasis for most tumors is the lungs, which is why we often recommend radiographs (x-rays) of the lungs when we are evaluating a cancer patient.

The treatment offered for a type of cancer depends on that cancer’s usual behavior. If it is a cancer that is very aggressive locally (ie. where it is first detected), then local treatments such as surgery, radiation therapy, and photodynamic therapy, will be used. If a tumor has a high chance of spreading throughout the body, then chemotherapy and sometimes immunotherapy (teaching the body’s immune system to recognize the cancer cells and destroy them) will be used. Some tumors cause problems both locally and systemically (throughout the body) in which case a combination of surgery and chemotherapy is often used. The prognosis for a given cancer with a given type of treatment will also vary by type of cancer.

An oncologist is a veterinarian who has completed additional training to specialize in the diagnosis and treatment of cancer. After undergraduate studies and four years of veterinary school, veterinarians must first complete a one year internship or at least 2-3 years in general practice before applying for a residency. A veterinary oncology residency is usually 3 years of additional study during which time in-depth education on the nature and treatment of cancer is completed. At the end of the residency, an examination is taken and with the completion of a certified residency, the successful passing of the examination and the publication of research in the field of cancer, a specialist is then board certified in the specialty of oncology.