Oncology Service

Oncologic Surgery in Small Animals

In order for surgical tumor removal to be successful, the surgeon need to have as much information as possible regarding the biologic behavior that can be expected of the tumor and the location of tumor cells, including the extent of the tumor in the surgery field, and the possibility of spread (metastasis).

What type and grade is the tumor?

Different types of tumors behave biologically very different. Some tend to grow very invasively, similar to a plant growing long roots in all direction. Some types of tumors tend to spread to distant places and organs (metastasize) rather than to grow invasively. A correct diagnosis of tumor type is very important for the surgeon in the planning of the surgical margins. An invasive tumor type is ideally removed with at least 3 centimeter margins (or roughly 1 inches) in all directions, including depth. That means that if the tumor itself is 2 inches in diameter, the tissue removed exceeds 4.5 inches in diameter. Therefore, wide or radical surgery often entails amputation if the tumor is located on or near an extremity. A tumor on the head might require removal of parts of the jaw or an eye to achieve clean margins.

If a surgeon is working together with an oncologist, such as at WSU-VTH, the oncologist has often obtained tissue samples (biopsies), by a smaller surgical procedure, to diagnose the tumor by histopathological examination before the final surgery. From a biopsy the tumor type can often be clarified, and in many types of tumors the pathologist can also give a grade, or an estimation of how aggressive the individual tumor is. Both the type and the grade of tumor are important when surgical margins are planned.

Where is the tumor?

Often the surgeon can only appreciate the most peripheral part of a tumor, the part that is visible externally. It is very valuable to know if the tumor is growing close to or even into important organs deep to the visible part. Diagnostic imaging is in general necessary for this reason. Regular x-rays are a good way to evaluate if bone is affected. However, the soft tissues are hard to evaluate from x-rays and computerized tomography or magnetic resonance imaging (MRI) are often better. The latter, MRI, is superior in the resolution of different soft tissues. An MRI can often give a good idea of how invasive the surgery needs to be.

The oncologist has in general made sure that there are no detectable signs of metastasis, before the surgeon performs a major procedure. However, if the dog or cat is very bothered by the tumor, due to pain or irritation, a surgical removal of a tumor might be indicated despite evidence of metastasis. It is important to understand that in that case the surgery will not stop or prevent additional growth of the metastases. It is also important to realize that metastases under a certain size (in general 3-5 mm) might be impossible to detect before a major surgery.

Surgery type

The surgeon can choose to perform these surgeries before diagnosis is obtained:

  • Insicional biopsy- one or several little pieces of the tissue are obtained for histopathological examination.
  • Excisional biopsy- the entire tumor is taken out for examination, without or with limited surgical margin. This is in general only done if the likelihood is high that the tumor is benign or the tumor is very small. If the tumor turns out to be malignant with a high likelihood of cancer cell invasion beyond what was removed, it can be much more difficult to define the appropriate margins in an additional surgery.
After tumor type is diagnosed, these surgeries are considered based on how much margin the surgeon can remove.
  • Intracapsular resection- Refers to tumor removal where some visible tumor is left behind. This is in general done due to the presence of important, non-resectable organs close to the tumor. Adjunctive treatment such as radiation is usually added after or before an intracapsular resection. Sometimes intracapsular resection is called cyto-reductive surgery or debulking.
  • Marginalresection- the tumor is taken out without margin, just outside the visible part. This leaves microscopic tumor behind, and just like after intracapsular resection, additional treatment is usually necessary.
  • Wideresection-a margin of visibly normal tissue is resected together with the tumor, in order to minimize the risk for leaving behind tumor cells. This is the most common type of surgery, when surgery is used as the only treatment for cancer. Many cancer types of low or intermediate grade can be successfully removed this way. A wide resection often entails wound reconstruction to enable closure of the wound or to ensure normal function. The reconstruction is planned before a major tumor removal and usually performed during the same anesthetic procedure. If skin reconstruction is extensive, the clipped area on the dog or cat can be big, and large areas sutured (or stapled).
  • Radicalresection- the entire structure the tumor is growing in is removed. This is commonly the case when amputation is an option, but harder to do on other locations than extremities.

Your surgeon and oncologist’s goals are always to give your pet the best quality of life of possible while attempting to eliminate the cancer. A surgery which may cure the tumor but is too aggressive for a pet to tolerate- would never be recommended.

In summary remember: it is important to know the type, grade and stage of you pets cancer before undertaking surgical resection. It may seem like additional test recommended are a waste of money but in actuality they are recommended to try and save money and heartache in the future. Also remember that after a major cancer surgery your pet may not be released form the hospital for 1-2 days and the incision you see may be much larger than you expected!

Washington State University