Canine Fibrosarcoma and Radiation

Lili Duda, VMD
Last Modified: November 1, 2001

Dear OncoLink "Ask the Experts,"
Our vet did a biopsy to remove a mass from our 7-year-old Boston Terrier. He has a well-differentiated fibrosarcoma located in his back right leg near his knee, she indicated that she did not think that it was cancerous. Therefore, she was not careful about getting all of the tissue around the mass on the first try. Unfortunately a second, more "aggressive" biopsy revealed that it was fibrosarcoma and that the margins were "free of tumor."

Our vet proceeded to tell us that at this point, we had two options:

  1. go ahead and proceed with radiation treatments to be sure that we dispose of the fibrosarcoma just in case microscopic pieces of the cancer remain, or

  2. wait for a period of 3-4 months (and thereafter for about 2 years) in which we keep a close eye on the area for re-growth of the tumor, if it does come back, then we can again have the tumor removed surgically and begin radiation treatments immediately thereafter.
He then told us that he is somewhat conservative and would seriously consider all alternatives to immediate radiation treatment.

As you might imagine, we are now in a strange position. We would rather not put our dog through the radiation process if it isn't needed, but we also want to do whatever it takes to cure him and give him the best chance at a complete cure. Therefore, my question to you is whether you agree with our vet when he says that the odds of a successful radiation remain as good if we wait as compared to immediate treatment, and what your suggestion would be as to our course of action?

I would like to thank you for your prompt response and helpful advice. My dog, my husband and I appreciate it more than you will ever know.  
Sincerely yours,

Lili Duda, VMD, Editor of the OncoLink Veterinary Oncology Section, responds:

OncoLink has a policy of not rendering professional opinions via e-mail, as it is impossible to render an accurate diagnosis/treatment plan without examining a patient in person.

However, in general it is difficult to get wide margins on soft tissue sarcomas that occur on limbs, a lot depends on the size and invasiveness of the tumor, where on the limb it is located, and how quickly the tumor was growing, as well as the size of the surgical margins. I usually formulate my treatment recommendations based on a physical exam (really the single most important piece of information) and an educated guess. The information you received from the second biopsy and opinion sounds similar to my own opinion. Regarding the biopsy report, while it is encouraging that the margins are reported as being free of tumor, it is not a guarantee (because of the way fibrosarcomas tend to grow), which is why some radiation therapists recommend radiating all soft tissue sarcomas. There is no right or wrong decision in this case because there are good arguments both ways. Theoretically, the first surgery is the best chance for tumor control, but practically, many people wait to see if the tumor grows back before pursuing aggressive treatment and these tumors can still be controlled.

If you elect "watchful waiting," the most important thing is catch tumor growth early, as the smaller the tumor, the better the chances of tumor control. Also, if the tumor is fairly slow-growing, it may not come back for months to more than a year.