Your pet has been diagnosed with cancer. Cancer is a disease that is due to the uncontrolled and purposeless growth of cells in the body. The terms cancer, malignancy, and neoplasia are synonyms.
Cancer is not a single disease since it can arise from any tissue in the body. Therefore, there are many types of cancer. Some forms of cancer have the ability to spread to other sites in the body which are often far from the original site. This occurs when cancer cells enter the blood or lymph vessels and are then carried to other organs. Cancers with this type of behavior are considered malignant.
Oftentimes, it is the spread of a cancer that causes the greatest problems. When a cancer has spread in this fashion, it is said to metastasize. Some cancers lack the ability to metastasize but may cause significant damage due to growth and invasion into local tissues. Tumors that do not metastasize and are not invasive are considered benign. The term, tumor, is a general word for cancer whether is is benign ("good" cancer) or malignant ("bad" cancer). Oncology is the branch of medicine dedicated to the study of cancer and the veterinarians treating your pet at VHUP are oncologists...
NB: In my practice I have had great success maintaining quality of life of cancer patients. I typically do not advise chemotherapy except is ome cases of lymphoma. In most cases, the survival stats and other scientific evidence do not support it in my opinion. Surgery and radiation are even less often useful in my opinion. Homeopathic palliation is the best path in my experience.--Dr. Jeff