Canine Cancer Prognosis

Tumor Growth

• A tumor in a dog can be either benign or malignant, and each offers its own challenge. When a veterinarian discovers a tumor, the first step is to examine a sample of it under a microscope, a process known as biopsy. Benign tumors usually exist within fibrous tissues, making them easier to remove surgically. Malignant tumors, at least in their advanced stages, exhibit no boundaries and invade into surrounding tissues. Whether a tumor is benign or malignant plays a role in prognosis, as malignant tumors are typically much more dangerous once invasion begins.

Malignant Tumor Types

• Malignant tumors in dogs are classified based on their embryonic origin, as there are three basic embryonic layers that normal animal cells develop from: the endoderm, ectoderm and mesoderm. Malignant tumors that are derived from the endoderm or the ectoderm are known as carcinomas, while tumors derived from the mesoderm are known as sarcomas. Another classification of malignant tumors is leukemias, which are a subdivision of the sarcomas.

Detection

• A positive cancer prognosis in a canine often depends on early detection, but this is one of the most challenging parts of dealing with cancer because not every cancer will present with a visible tumor. Malignant tumors can appear within the organs of the body instead, eventually causing symptoms like diarrhea and vomiting, gastrointestinal bleeding and neurologic symptoms, but it is often once the cancer has progressed significantly in terms of staging.

Diagnosis

• The most common method of diagnostic imaging in veterinary medicine is survey radiography or X-ray. This technology can show the position, size, shape and density of a cancerous growth. Another option is computed tomography or CT scan, which is not always available in veterinary medicine but is still a viable alternative. A veterinarian may also use magnetic resonance imaging or MRI scanning or ultrasound, as these are also non-invasive methods for getting an image of the cancer. Once the cancer is detected, the next step is staging.

Staging

• Staging defines the extent that the cancer has spread throughout the dog's body. This is the most necessary step in assessing a cancer prognosis and selecting the proper therapies accordingly. There is a clinical staging system for each type of cancer. Solid tumors have three different categories, with "T" denoting the size, "N" denoting the level of invasion of lymph nodes and "M" for metastases. Four clinical stages exist beyond these categories, with stages I, II and II indicating local disease, local disease with regional spread and local disease with extensive spread respectively. Stage IV is meant to indicate stage I, II or III cancer with metastases in distant sites. Prognosis typically becomes less favorable with each advancing stage.