THE MOST COMMON TUMOR TYPES
TREATED BY RADIATION THERAPY

Deborah M. Prescott, DVM, PhD
Diplomate ACVR in Radiation Oncology
Director, MedVet Radiation Oncology Center

The cancer types most often referred to MedVet’s Radiation Oncology Center, and the methods of treatment, are as follows:

Skin and Subcutis Tumors

Since the majority of skin and subcutis tumors are benign, surgery is clearly the primary method of treatment. However, 20% of canine and 40% of feline skin tumors are malignant ( such as mast cell tumors, squamous cell carcinomas, hemangiosarcomas, and melanomas). Radiation therapy should be considered in these patients, especially when surgical excision of the tumor is incomplete, resulting in microscopic tumor cells being left behind at the surgical site.

Nasal Tumors

Nasal tumors tend to be locally aggressive with survival of these patients limited by local recurrence. Surgery alone is generally not effective because of the complex anatomy. Radiation therapy is the treatment of choice for long-term tumor control.

Oral Cavity Tumors

The oral cavity is the fourth most common location for canine and feline cancer.  Approximately 50% of oral tumors are malignant.  Radiation therapy is an important method of treating feline and canine malignant oral tumors and is often combined with surgery or chemotherapy.  The remaining 50% of canine oral lesions are benign, but can be locally invasive into bone such as acanthomatous epuli.  Although surgery alone can control these benign lesions, radiation is also effective and should be considered when the extent of surgery needed for control would alter function or be too disfiguring.

Soft Tissue Sarcomas

Because of their similar clinical presentation and biological behavior, it is convenient to consider soft tissue sarcomas as a group. This tumor classification includes histologies such as:

• fibrosarcoma
• hemangiopericytoma
• liposarcoma
• myxosarcoma
• undifferentiated sarcoma
• rhabdomyosarcoma
• neurofibrosarcomas (schwannomas), and
• malignant fibrous histiocytoma

Due to the locally-invasive nature of soft tissue sarcomas, surgery must be aggressive and often radical (e.g. amputation) to control the tumor.  In human soft tissue sarcomas, the combination of radiation and surgery is a common strategy and results in 80% to 90% local control while achieving acceptable cosmetic results.  Accordingly, progressive veterinary cancer Centers often combine radiation therapy and surgery to achieve the highest possible levels of local control.  In addition to radiation and surgery, chemotherapy is often used to control distant metastases, particularly for high-grade soft tissue sarcomas.

Brain Tumors

The most common brain tumors are meningiomas and glial cell tumors. The role of radiation therapy for CNS tumors is clearly established in human medicine and is becoming more important in veterinary medicine. The increased use of radiotherapy for the treatment of brain tumors has resulted in significant extension of a high quality life for these patients compared to other therapies that do not attempt to eliminate the primary tumor but only address the clinical symptoms.

Bone Tumors

Primary bone tumors are usually accompanied by pain. Although treatment of primary bone tumors with curative intent often alleviates such pain, there are some patients where curative treatment is not feasible or not elected by the owners. Alleviation of the pain associated with the tumor can make the patient more comfortable. In humans, radiation therapy is well established as the treatment of choice for localized bone pain from metastatic disease. Palliative radiotherapy plays a role in alleviating the pain associated with primary bone tumors. The concept of palliative radiation therapy can easily be applied to other tumors in an effort to improve the quality of a pet's life.

© 2005 Deborah M. Prescott, DVM, PhD, DACVR(RO). 
All Rights Reserved.