Tumors receive their blood supply from arteries whereas the blood exiting a tumor is drained via veins. Chemotherapy that is injected into blood vessels is most often administered into a vein. Chemotherapy given into a vein travels to the heart, through the pulmonary blood vessels and then to the tumor.
In select cases, chemotherapy may be administered directly into the artery (intra-arterial chemotherapy) supplying a tumor. The reason for giving chemotherapy by this method is to treat the tumor with the chemotherapy first before it travels throughout the body. In humans, this technique has been shown to increase the intra-tumoral chemotherapy concentration (the chemotherapy concentrated within a tumor) and may decrease side effects. Intra-arterial chemotherapy is not recommended for all cases, but it may be considered in certain instances. Due to the increased technical aspect of the procedure, anesthesia and a small incision are required to perform this procedure.
The administration of intra-arterial chemotherapy can be considered for many tumor types, and tumors commonly being treated at the UC Davis Veterinary Medical Teaching Hospital include tumors of the lower urinary tract (bladder/urethra/prostate), liver tumors and nasal tumors.
Intra-arterial chemotherapy is the delivery of chemotherapeutics into the tumoral arterial blood supply. The goal of this treatment is to evaluate the vessel/s most responsible for supplying the tumor and select those vessels with guidewires and catheters so that chemotherapy can be delivered directly to the tumor. The theory behind this technique is that intra-arterial delivery of the drug will increase the intra-tumoral chemotherapy concentration and decrease the side effects associated with chemotherapy.
The vascular approach to the tumoral blood supply will depend on the tumor location. Each dose is given under general anesthesia as fluoroscopy and precise positioning is necessary for effective selection of the vessels. Multiple treatments may be performed if the patient is tolerating each individual treatment.
These cases will first be assessed by our medical oncology team. If deemed a candidate, the use of interventional radiology as a treatment modality may be considered. Initial diagnostics performed at UC Davis may include bloodwork (complete blood count, chemistry panel, coagulation panel), chest radiographs, abdominal ultrasound, and computed tomographic examination of the tumor. Upon determining that a patient is a candidate for intra-arterial chemotherapy (and can tolerate chemotherapy), anesthesia will be induced, and the procedure will be performed. Further treatments will be planned at certain intervals depending on the chemotherapy that is being administered.
Embolization is a procedure that involves the injection of an agent that causes formation of an embolus (“clot”) in the blood vessel/s supplying a tumor. A chemoembolization procedure is when an embolization is combined with chemotherapy administration. The purpose of forming the embolus is to eliminate or decrease the blood supply to the tumor thus dampening the nutrient supply to the tumor. This procedure is generally only recommended in cases where surgical removal of a tumor is not possible. Examples of these may include large liver tumors, body wall tumors, nasal tumors, prostate tumors and tumors in locations where surgery may overly compromise a pet.
The performance of embolization or chemoembolization can be considered for many tumor types, and tumors commonly being treated at the UC Davis Veterinary Medical Teaching Hospital include liver tumors and nasal tumors.
Surgery is the treatment of choice for tumors that are deemed resectable. Occasionally, tumors may be found in a location that surgery is not recommended. Further, some tumors may be so large that surgical resection is unlikely to provide an acceptable outcome. In these cases, radiation therapy is often considered. For those cases where surgery and radiation are not elected, embolization or chemoembolization can potentially be offered.
Chemoembolization is a treatment involving delivery of a chemotherapeutic drug in combination with an agent that stimulates thrombosis. The goal of chemoembolization is to deliver chemotherapy into a vessel that is directly supplying a tumor. This direct delivery will increase the intra-tumoral concentration of the drug, and potentially decrease systemic side effects. When combined with an embolic agent, the vascular supply to the tumor can also be diminished. Further benefit of the embolic agent is decreased perfusion to the tumor and thus decreased elimination of chemotherapy from the tumor.
Chemoembolization is performed under general anesthesia and requires the use of fluoroscopy. Chemoembolization requires precise vessel selection via guidewires and catheters; knowledge of vascular anatomy is essential. Chemotherapy may be mixed with the embolic agent or may be delivered prior to injection of the embolic agent. Often, several treatments are necessary. Chemoembolization will likely not stimulate a complete response, but instead the goal is to decrease the size of the tumor (decreasing morbidity) and potentially increase the chance of resectability.
Diagnostic and Treatment Steps at UC Davis
These cases will first be assessed by our medical oncology team. If deemed a candidate, the use of interventional radiology as a treatment modality may be considered. Initial diagnostics performed at UC Davis may include bloodwork (complete blood count, chemistry panel, coagulation panel), chest radiographs, abdominal ultrasound, and computed tomographic examination of the tumor. Upon determining that a patient is a candidate for embolization or chemoembolization (and can tolerate chemotherapy), anesthesia will be induced, and the procedure will be performed. Further treatments may be necessary, and computed tomography may be performed at these future visits as well.