Assessment of response

Guidelines have been developed to avoid arbitrary decisions in assessing therapeutic response. Responses must be viewed in context with the original intent of therapy, whether it be cure or palliation. The RECIST (Response Evaluation Criteria in Solid Tumours) model for canine tumors specifies the following response criteria:

• Complete response: 100% resolution of tumor.
• Partial response: >30% reduction in overall tumor(s) size.
• Progressive disease: >20% increase in overall tumor(s) size.
• Stable disease: <30% reduction, <20% increase in tumor(s) size.²³

The Lymphoma Response Evaluation Criteria for dogs specifies the following response criteria:

• Complete response: Complete regression of all evidence of disease, normal-size lymph nodes.
• Partial response: >30% reduction in mean longest dimension of lesions.
• Progressive disease: >20% increase in size in mean longest dimension of lesions.
• Stable disease: <30% reduction, <20% increase in size of lesions.²⁴

Post-radiation therapy monitoring

Many patients have a good-to-excellent prognosis following initial radiotherapy. However, it is imperative for these patients to have periodic post-therapy examinations due to the possibility of recurrence, metastasis, new tumor development, or complications of initial therapy. Upon completion of initial therapy, patients are often restaged to determine extent of disease. Some tumors can take mo for the maximum treatment response to occur, so patience and ongoing supportive care is advisable. Partial response or stabilization of the growth of the primary tumor, leaving residual disease, may be the maximum post-therapy response seen.

Maintenance chemotherapy

For many oncology cases, initial therapy is done to prolong survival even though it is not considered curative. Additional chemotherapy, metronomic chemotherapy, or TKIs and cyclo-oxygenase inhibitors (COX-2) have been used as ongoing therapy in such cases. Use of the latter two agents is justified by their antiangiogenic properties as well as their anti-proliferative effects.^25,26

Management of recurrent or metastatic disease

The concepts that apply to maintenance chemotherapy are relevant to managing recurrent or metastatic disease. Pet owners should be prepared for repeat imaging and staging prior to final treatment decisions. Assessment of the patient’s quality of life is needed at this critical juncture because of the guarded prognosis and likelihood that a return to normalcy may not be possible. Goals of therapy in such cases are often dynamic and are obviously impacted by extent of disease and expectations for the patient’s quality of life.