Comparison of perioperative versus postoperative intratumoral administration of cisplatin for treatment of cutaneous sarcoids and squamous cell carcinomas in horses

Objective-To determine the benefits of reducing the interval between surgic al cytoreduction and intratumoral administration of cisplatin. Design-Randomized clinical study. Animals-70 horses with 89 incompletely resected T2- and T3-stage sarcoids ( n = 64) and squamous cell carcinomas (25). Procedure-Horses were given 4 intratumoral treatments of cisplatin at 2-wee k intervals. The first treatment was given at the time of, or immediately a fter. surgical resection for horses treated in accordance with the perioper ative protocol (group 1). Horses in group 2 were treated with cisplatin aft er the skin healed following surgical resection in accordance with the post operative protocol. Results-A difference was not found in duration of overall local tumor contr ol between the 2 groups. Patterns of treatment failures and interval to fai lure differed between the 2 groups. Length of the surgical scar was the onl y factor that affected prognosis; an increase in length was associated with a poorer prognosis. A detrimental effect of postoperative treat ment was o nly found in tumors with a high tumor proliferative fraction. Local reactio ns were similar for the 2 treatment groups, and chronic reactions were not observed. Conclusions and Clinical Relevance-Intratumoral administration of cisplatin is beneficial for treatment of cutaneous tumors in horses. Tumor repopulat ion during the interval between surgery and intratumoral administration of cisplatin decreases treatment efficacy. These results provide evidence of r apid tumor repopulation following surgical resection without a lag period f or tumors with a high proliferation index. When tumor proliferation index i s not known, it may be prudent to use the perioperative protocol.