DEFINING TREATMENT OPTIONS for YOUR PET
The decision making process for management of cancer in pets can be a complicated and difficult process. The evaluation of the general health of the patient, the type of cancer, access to specialized treatments and the emotional, time and financial commitment to conduct the treatment must be carefully considered. The benefits, risks and costs cannot be adequately determined without some assistance and support. Such support is best obtained from family, friends and veterinary professionals. Once the general health of the patient has been determined to be adequate and the cancer has been clinically staged and biopsied, the next decision is to determine treatment options.
TUMOR BIOLOGY and NATURAL HISTORY
Rational treatment planning involves basic knowledge of the potential for local recurrence and metastasis of the neoplasm. The keystone of this information is the histological assessment or diagnosis. Malignant tumors predisposed to local recurrence should be managed aggressively from the time of initial diagnosis. The chance for long-term tumor control is greatest when the tumor is undisturbed by previous therapeutic intervention. The risks and benefits of aggressive management must be carefully considered. However, most people will recognize the obvious benefit of prolonged tumor response with reduced overall expense if the tumor can be managed once, albeit initially more costly, compared to multiple, suboptimal attempts at tumor control.
GOALS of TREATMENT
Maintaining the highest quality of life for the longest period of time is always the goal of cancer management in companion animals. This goal must be considered within the context of emotional and financial factors. Decisions are often difficult.
The best service that can be provided is a knowledgeable, unbiased assessment of the condition and a frank discussion of options sufficient to permit an informed decision. This may involve consultation or referral to a specialist or a comprehensive cancer center. Curative therapy is designed to attempt permanent control of the tumor using aggressive but not excessively debilitating treatments. Multiple treatment modalities are often employed.
The decision to pursue curative treatment can be difficult. A working definition of curative therapy often used in veterinary medicine is the likelihood that a given tumor type will be controlled for at least 1 year following treatment. If the best available information suggests this is not possible, palliative therapy may be considered.
Palliative therapy is designed to reduce pain or functional difficulties such as swallowing, urinating or defecating without attempting to cure the tumor. The length of time is not as important as the quality of the time remaining for the pet. The hospital time and side-effects must be minimal for palliative therapy. Pets with cancer may also require Œsupportive therapy¹ such as antibiotics, medications to control some symptoms, blood transfusions and nutritional management.
The first therapeutic determination made by the veterinarian involves whether the tumor may be completely excised. This is determined based on the size of the surgical field necessary to remove all known and probable tumor extent, the site of the tumor and the skill of the surgeon.
The site of the tumor dictates the extent of normal tissue resection. For instance, interscapular injection-site sarcomas in cats require extensive removal of tissue, including portions of dorsal vertebral processes and scapulae, due to the complex nature of the fascial planes within that site. Regions where sufficient normal tissue cannot be removed (e.g., distal extremities, skull) may require extensive reconstruction (grafting) or consideration of multimodality therapy. More sophisticated tumor imaging techniques, such as CT or MR, greatly assist presurigcal planning for invasive tumors or for tumors located close to critical normal structures. The skill and experience of the surgeon is extremely important. Removal of tumors and reconstruction of normal tissue in difficult locations requires skills that must be continuously practiced and updated.
Some tumors are radiation sensitive (e.g., acanthomatous epulis, plasma cell tumors, mast cell tumors) and may be considered potentially curable if they are located within a site that is not amenable to complete resection. A combination of radiation and surgery improves outcome in situations when neither treatment modality alone is sufficient to accomplish that goal. Well-planned, combined modality therapy is being used more frequently for tumors which are located in difficult sites.
The ability to achieve a curative outcome is based on assessment of the natural history of the specific tumor typed as defined by clinically relevant predictive indicators (i.e., grade) and the available treatment options. The need for adjuvant therapy (secondary to initial treatment) is based on incomplete resection of the tumor, a high likelihood of local tumor recurrence following resection or a high rate of metastasis even if the primary tumor is permanently controlled. One of the most important aspects of tumor treatment is determining if the margins of normal tissue surrounding the resected tumor contain tumor cells that extend to the edges. This aspect of the surgical management of cancer should be taken very seriously since it may influence the need for additional treatment with chemotherapy, immunotherapy or radiation therapy.