Tips for managing cancer patients in general practice, and when to refer (Proceedings)


Tips for managing cancer patients in general practice, and when to refer (Proceedings)

Nov 01, 2009

Diagnostic approach to pets with cancer

Dogs and cats with cancer are typically presented by their owners either because of the physical presence of the mass if it is visible or palpable, or because of the effect of the cancer on the body and its functions. Neoplasia is defined as new growth. Cancer is the state of having a neoplasia in the body. Malignancy is generally reserved for those cancers that have some ability to metastasize, whereas benign cancers are strictly local lesions. A "tumor" is generally considered a solid neoplasia, as opposed to a hematogenous neoplasia such as leukemia. It is important to establish the owner's knowledge base and understand where they have gained that knowledge in order to best communicate with them about the approach to their pet's diagnostic work up.

When presented with a sick animal, if physical examination fails to reveal a mass, minimum database should include complete bloodwork, and radiographs and ultrasound should be offered. If a tumor is found, it should be needle aspirated if it is accessible. If the mass is in a body cavity, ultrasound guidance may be necessary. Needle aspirates of urinary tract masses should be avoided if at all possible, as seeding of carcinomas to the abdominal wall has been seen. An incisional biopsy should be performed if the information will change the treatment or change the owner's willingness to treat. Biopsies should be performed such that the biopsy tract can be removed with the tumor at the time of definitive treatment.

A general practitioner may also be asked to "screen" a pet for cancer. The diagnostics listed above constitute a logical approach to such a pet, however it must be emphasized to the owner that there is no definitive test to say whether or not a pet has cancer. Screening tests such as cancer antigen levels commonly available in human medicine are not routinely available in veterinary medicine. There are however tests that may help screen a geriatric patient for specific cancer as in the case of the VBTA (veterinary bladder tumor antigen) test for bladder cancer or in serum tests such as calcium levels (can be elevated in lymphoma and anal sac adenocarcinoma) or alkaline phosphatase (can be elevated with osteosarcoma). It is important to understand the limitations of these tests in order to apply them to a given animal patient.

Cancer treatment

Including an oncologist in the evaluation and treatment planning of a pet with cancer can improve patient outcome, as well as satisfaction for both the client and the general practitioner. A referral may be necessary if equipment required for treatment is unique and not routinely available. The primary treatment modalities for treating cancer are surgery, radiation and chemotherapy. While radiation facilities are limited due to the equipment required, both surgery and chemotherapy can be performed in private practice. Surgery and radiation are used for local control of cancer, whereas chemotherapy can be used to improve both local and systemic control.

Unique toxicities of selected chemotherapeutic agents
Chemotherapy is not difficult to administer, but a commitment to understanding the drugs, necessary administration precautions, and each drug's side effects is critical. Some drugs are vesicants and can cause severe tissue sloughing if not properly administered. Even if the general practitioner chooses not to include injectable chemotherapy in their practice, there are oral chemotherapy agents that can provide treatment options to a client without the need for travel to a specialist. For some general practitioners, a referral for comprehensive cancer treatment is the best option, whereas in other practices a great deal of cancer care can be done in-house with periodic communication with a local specialist or teaching hospital.