Brooke Fowler, DVM, MS, DACVIM (Oncology)
For decades, the mainstay of cancer therapy has been chemotherapy for systemic disease, one that affects multiple organs and tissues, and radiation or surgery for locally invasive tumors. Sometimes, however, tumors do not fit neatly into these treatment categories. After all, cancer is wily, unpredictable, and likes to follow its own rules. Local disease burden seems to be the most difficult type of tumor to deal with. Many of these tumors are not recognized for early intervention or grow in locations that rapidly make them difficult to treat surgically. So, what are the available treatment options for these tumors?
Surgery has been and always will be the most direct and ideal way to treat locally invasive tumors. There are circumstances, however, where the tumor has grown in a location that makes it difficult to cut or to achieve clean margins. In surgery, the surgeon hopes to remove the entirety of the tumor, as well as a buffer of healthy tissue to ensure all of the cancer has been removed. When clean margins cannot be achieved, the tumor becomes more susceptible to regrowth. Radiation is considered the standard of care for the majority of incompletely excised tumors. Unfortunately, radiation is costly both in terms of dollars and time that the patient and owner must commit to undergo this treatment regimen. Chemotherapy is rarely considered an ideal option to treat local disease as this is a systemically administered therapeutic. Many chemotherapy drugs are administered intravenously or may be given orally and these routes of systemic administration will affect the entire body. Therefore, these chemotherapy drugs come with potential systemic side effects when treating a local disease burden.
Figure 1.Electrochemotherapy Unit
A new and exciting alternative therapy to treat local disease is electrochemotherapy. This treatment option involves the use of small doses of systemic or intralesional chemotherapy followed by electric pulses applied to the tumor. In contrast to systemic administration, intralesional chemotherapy is injected directly into the tumor, helping to minimize the potential systemic side effects. Electric pulses, in turn, allow the pores of the cells to open, allowing higher doses of chemotherapy to be absorbed into the cancer cells. This electroporation, as it is called, makes the cells much more efficient at absorbing chemotherapy. Additionally, this treatment option has provided new uses for medications previously known to be toxic in certain species.
The treatment of these tumor cells results in apoptotic cell death. As cell death occurs, fragments of the cell, known as apoptotic bodies, are engulfed by neighboring cells and removed. This helps prevent further damage that can be caused be the cancerous cells, which, in turn, decreases the local side effect and even the possibility of tumor presentation to the immune system. This theoretical situation allows for the possibility that the body may be better able to fight metastatic disease, or the spread of the disease to other organs.
This treatment is ideally used post operatively. When possible, the bulk of the tumor will be removed surgically prior to administering electrochemotherapy. Electrochemotherapy will be performed on incompletely excised tumors, in which clean margins were not achieved, leaving behind cancerous cells that may promote tumor regrowth. This treatment option can be used intraoperatively, as well, when surgical removal of the entire tumor seems unlikey.
Tumor types which have shown promise for this treatment include mammary tumors in cats and dogs, mast cell tumors, vaccine associated fibrosarcomas in cats, localized lymphoma, and papillomas. Studies performed analyzing the efficacy of electrochemotherapy in treating these types of tumors have shown success, some even rivaling the outcomes seen with radiation therapy.
Aspen Meadow Veterinary Specialists is excited to announce that we recently introduced electrochemotherapy to help treat cancer in our patients. This treatment is performed on an outpatient basis, requiring 2-3 treatments depending on tumor response. While radiation therapy will always be the standard of care for the majority of incompletely excised tumors, electrochemotherapy offers a more cost effective alternative, while potentially providing outcomes that can be comparable to traditional radiation therapy.
There is much we have yet to learn about cancer and the treatment of these tumors is constantly changing. We are glad to have one more tool available in our toolkit that can be used to help treat cancer in our patients.
Dr. Brooke Fowler is an oncology specialist at Aspen Meadow Veterinary Specialists. AMVS is a 24-hour veterinary facility providing specialty internal medicine, surgery, neurology, oncology, emergency and critical care, physical rehabilitation, and blood bank services for pets. They are located in Longmont at 104 S Main St. For more information, go to www.AspenMeadowVet.com.