Introduction to Oncology
Oncology is the study and treatment of cancer, and their related diseases. “A neoplasm or tumor is an abnormal uncontrolled growth of cells which develop faster than the surrounding normal tissues.”
Most tumors appear as our canine and feline patients start to age. It’s common to start seeing tumors at 8-10 years of age, and at 5 years of age in our giant breeds. There are some very aggressive tumors which can occur in animals as young as a few months old. There are certain breeds that are susceptible to tumors, such as Boxers and mast Cell Tumors and Flat Coated Retrievers and sarcomas. Neoplasia can be either benign or malignant.
Benign tumors often grow slowly and are discrete and encapsulated. They are often free moving from surrounding tissues.
Lipoma - A fatty tumor usually composed of mature fat cells.
Papilloma - A tumor derived from epithelial cells, most often seen on the skin but can also occur in the bladder, rectum and oral cavity.
Melanoma – A pigmented skin tumor of melanocytes. Keep in mine some melanomas can be highly malignant.
Fibroma – A tumor composed mainly of fibrous tissue, may be difficult to differentiate from other malignant skin tumors.
Adenoma – A tumor of glandular tissue.
Malignant tumors may either grow quickly or slowly. They may have a defined capsule and be attached to surrounding tissues. These tumors can also metastasize to other organs such as the lungs, spleen, liver, bone, and/or brain. The rate of metastasis varies by tumor classification.
Carcinoma – A malignant tumor arising from epithelial cells.
- Squamous cell carcinoma – Oral cavity
- Transitional cell carcinoma – Bladder
- Adenocarcinoma – Glandular tissue in epithelia
Sarcoma – A malignant tumor arising from mesenchymal tissues
- Lymphosarcoma – Lymphoid tissue may be associated with feline leukemia virus in cats.
- Fibrosarcoma – Arises from fibroblasts and may be found in connective tissue.
- Osteosarcoma – Tumor of osteoblasts and is usually in the limb bones.
Proper classification of a tumor, by histopathology, must be done so a diagnostic plan can be prepared. All patients must have radiographs taken prior to anesthesia to see if there are any signs of metastasis. The radiographs should include a right and left lateral chest, v/d chest, right lateral abdomen, and v/d abdomen to be complete. Once the histopathology is read a CT scan or MRI may be indicated.
There are different ways of obtaining a tissue for histopathology.
- Fine-needle aspirate – FNA can be used to screen primary lesions for the presence of cancer, or in the staging process to determine whether lymph nodes or other secondary sites are involved.
- Bone marrow biopsy – Aspirates are used to remove a bone marrow sample using a bone marrow needle.
- Needle core biopsy – A small cylinder of tissue is obtained using a specialized instrument such as a Tru-Cut needle.
- Punch biopsy – Punch biopsies are taken using small circular cutters, from superficial lesions in the skin.
- Trephine biopsy – Trephine biopsies are taken from bony tumors using a Trephine or a Jamshidi needle.
- Incisional biopsy – A wedge of tissue is taken from a part of the tumor that appears to be actively growing and then the wedge is repaired with sutures.
- Excisional biopsy – This is usually used for small tumors that are easy to remove with a margin of normal tissue, particularly if it is suspected the tumor is benign.
- Endoscopy – These samples are very small and are best handled with a fine-gauge needle.
Benign tumors can often be completely cured by excisional surgery. Malignant tumors can be either debulked, fully excised or partially excised and then will require follow up treatment. Palliative surgery may be performed to remove a tumor to improve the animal’s quality of life although it does not alter the prognosis.
Some follow up treatment options:
- Cryosurgery – is where the tumor is destroyed by freeze-thaw cycles that cause the cells to rupture due to ice crystal formation. This is not selective and normal cells are also killed.
- Chemotherapy – is the use of cytoxin drugs to kill tumor cells selectively.
- Radiotherapy – is used in specialist centers to kill dividing tumor cells
- Hyperthermia - is a technique that uses local application of heat via needles introduced into the tumor to try and kill the dividing tumor cells.
- Most if not all malignant tumors will require a multimodal approach, including but not limited to analgesia, nutritional support, antibiotics, anti-inflammatories, and nursing care.
Oncology for Veterinary Technicians and Nurses – Moore and Frimberger
Veterinary Nursing – Lane and Cooper
Dorland’s Pocket Medical Dictionary