Cancer Facts for Pet Owners

Normal cells have a limited number of cell division before their DNA (genetic makeup) is damaged leading to automatic cell death (cell suicide). Tumor cells are immortal having no checks and balances on their number of cell divisions.

Cancer is a genetic disease that can be affected by environmental influences that increase the likelihood of developing cancer. The initiating causes are a series of genetic changes in the DNA of the cell. Normal cells change into cancer cells when there are mutations (changes) in the DNA of the cell. Three classes of cellular genes are affected by the mutation. Oncogenes prevent tumor formation. If altered they lose that ability. Tumor suppressor genes regulate cell growth. When altered, they lose that regulatory function. DNA repair genes are there to repair mutations in other genes when they occur. If damaged, they are unable to repair other cellular DNA. These three sets of genes are there to put the breaks on cell growth. Once they lose their function, cell growth can progress unchallenged leading to cancer.

Once the damaged cell’s growth has started, environmental influences such as ultra-violet light, chemicals, viruses, cigarette smoke cause the damaged DNA to go from bad to worse. This starts a rapid, unchecked cell growth leading to tumor formation.

Tumors spread by inducing blood and lymphatic vessels to grow into the tumor supplying nutrients necessary to fuel the rapid cell production. Once the vessels grow into the tumor, the tumor cells invade the lining of the vessels gaining access to the blood stream. Cells then flake off the tumor and are transported all over the body. The majority of these cells are killed by turbulence in the blood stream. Only about 0.1 percent survive the trip. If the microcirculation of the new organ is favorable, the cancer cell starts to grow there starting the tumor process over in another part of the body. This type of tumor is malignant and the spreading process is called metastasis. Some organs support tumor cells better than others. That is why most tumors spread to the lungs and liver.