CANCER

Cancer as an Angiogenesis-Dependent Disease

Tumors are categorized into two types: benign and malignant. A benign tumor is noninvasive at the site of origin (it grows in the tissue layer in which it starts and does not invade other layers or surrounding tissues), is not cancerous, and does not metastasize (spread to other locations in the body). A malignant tumor is a cancer, and it invades local tissues and has the potential to metastasize via the bloodstream or lymphatics to other sites in the body.

Cancer cells produce angiogenic growth factors that stimulate new blood vessels to sprout from pre-existing healthy blood vessels and grow into the tumor. Once new blood vessels enter the tumor:

  • The tumor is able to rapidly expand in size (up to 16,000 times in 2 weeks)
  • The tumor can invade local tissues and organs, disrupting normal function
  • Cancer cells are shed through the new blood vessels into the circulation as metastases

Cancer in Dogs

Cancer is the most common cause of death in pet dogs, according to a 1998 JAVMA article. The occurrence of canine tumors increases with age, and pets over the age of 10 are the most prone to tumors. Younger animals, however, are not immune to cancerous growths. The most common cancers in dogs are lymphoma, osteosarcoma, soft tissue sarcomas, oral melanoma, and mammary carcinoma. All are dependent on angiogenesis for their ability to grow and spread.

Methods of diagnosing canine cancers vary according to the tumor type, but the common tests used by veterinarians include radiographs, blood tests, physical examination of a suspected mass and its location, and often a surgical biopsy. The biopsy enables a precise histopathological diagnosis to be made. Research is now being conducted at the Angiogenesis Foundation to determine if blood tests designed to measure angiogenic growth factors (VEGF and bFGF) can assist in early detection.

Cancer treatments for dogs vary as well, and may include one or a combination of the following: surgical excision of the tumor, chemotherapy, radiation, and (rarely) cryosurgery or immunotherapy . Antiangiogenic therapy, designed to cut off the tumor blood supply, is now being developed to treat canine cancers. Unlike chemotherapy, antiangiogenic treatments are well-tolerated, have few side-effects, and may control disease over the course of the dog's lifetime.