Vaccine-associated sarcomas have been discussed in the literature for several years. Surgical excision of these neoplasms has reportedly achieved variable, but limited success. Of those cats treated surgically, time to first recurrence of the tumor has ranged from 94 - 325 days (~3 - 10 months), with a median overall survival time of 576 days (~19 months). Less than 14% of the cats receiving surgery alone survived greater than 2 years. Cats with neoplasms located on the limbs had longer time to recurrence than cats with neoplasms at other sites. (A.E. Hershey, K.U. Sorenmo, M. J. Hendrick, et al.; JAVMA 216 (1), pp. 58-61, January 1, 2000.)

In an effort to improve the prognosis of 18 cats affected with vaccine-associated sarcomas, iridium-192 temporary interstitial implants were utilized post-surgically to irradiate their tumor excision sites. Pathology diagnosis of the tumors included: fibrosarcoma (15), soft tissue sarcoma (1), giant cell tumor (1), and myxosarcoma (1). Radiation doses utilized were: 4000 cGy (2), 4,500 cGy (4), 5,000 cGy (7), and 6,000 cGy (5). Implant time was 5 days (1), 6 days (2), and 7 days (15). Treatment field size varied, with a mean and s.d. of 62 +/- 32 sq.cm.

Present results are preliminary, and follow-up of the patients response to post-surgical iridium-192 brachytherapy continues. As of 8/2000, results include: tumor recurrence by 5 and 6 months (4000 cGy); recurrence by 8 months (4,500 cGy), no recurrence by 5, 5 and 9 months (4,500 cGy); no recurrence by 6, 14, 14, 14, 14, 24 and 42 months (5,000 cGy); recurrence by 4, 6 and 7 months (6000 cGy), and no recurrence by 6 and 8 months (6,000 cGy).

Generally, the tissues tolerated the treatment well. Reported tissue reactions included: change in hair color, hair loss or slow hair regrowth (9), wound dehiscence (5), and seroma formation (1).

Based on these preliminary results, iridium-192 appears to be an acceptable form of adjunctive therapy for vaccine-associated sarcomas in cats.