Successful treatment of an equine preputial fibrosarcoma using 5-fluorouracil/evaluation of the treatment using quantitative PCNA and KI67 (MIB 1) immunostaining (Case report)

An 18-month-old cross-bred Fjord pony colt presenting a fibrosarcoma of the prepuce with severe infiltrative growth, was treated by topical applicatio n of 5-fluorouracil. Biopsies were taken before and after a treatment perio d of 2 months. As a control, preputial tissue from a healthy horse was biop sied. Tissue sections were stained immunohistochemically for Proliferating Cell Nuclear Antigen (PCNA) and Proliferation related factor - Ki67 (MIB1). Using computerized quantitative image analysis of these sections, Mitotic index (PCNA), Growth Fraction (Ki67) and total nuclear area percentage of t he dermis were calculated. The Mitotic index, growth fraction and total nuclear area percentage were s ignificantly (P < 0.001) reduced at the end of the treatment period compare d to the initial biopsy tissue, bur they still were significantly higher th an the control values, due to a remnant inflammatory reaction to the cytost atic drug. After treatment of the lesion, the pony fully recovered with no visible residual lesions on the prepuce. On follow-up 6 months after treatm ent, the horse showed no signs of recurrence. The success of the present treatment should encourage further clinical tria ls in cases of malignant fibrous rumours of skin in horses. The quantitativ e analysis of cell proliferation in biopsies can be used to evaluate treatm ent follow-up.