Ki67 Reactivity in Nasal and Periocular Squamous Cell Carcinomas in Cats Treated with Electron Beam Radiation Therapy

Abstract

Squamous cell carcinomas of sparsely haired skin are relatively common tumors in cats, and these tumors likely exhibit a rapid growth rate. Thus, we evaluated response and duration of response in relation to the Ki67 proliferative reactivity in such tumors. Seventeen cats with confirmed squamous cell carcinomas and treated with an accelerated, hypofractionated electron beam radiation protocol were included in the study. For all of them histologic grading, Ki67 reactivity, response, and disease-free interval (DFI) were evaluated. Response to therapy was excellent (94% complete response rate) with a median DFI of 414 days. Only moderate acute and few long-term adverse effects were seen. Cats with tumors with a low Ki67 reactivity had markedly shorter DFIs than cats with tumors with high Ki67 reactivity. We concluded that an accelerated, hypofractionated electron beam radiation therapy protocol is well suited for feline squamous cell carcinomas. The protocol appears especially efficacious in tumors with a high Ki67 reactivity.

Retrospective clinical study on outcome in cats with nasal planum squamous cell carcinoma treated with an accelerated radiation protocol

“…The outcomes of patients with cSCC of the nasal planum reported in a previous study by our group ( n  = 12) were reassessed over a longer follow-up period and included as well. [3] Adequate available follow-up consisting of tumor response, date of recurrence or systemic progression as well as date and cause of death was required.…”

“…Pathologic diagnoses and grading were made by an experienced pathologist (FG) as described previously. [3, 18] In brief, three grades (I, II, and III) were distinguished, with more malignant morphology indicated by higher grades. The following characteristics were scored based on a scale: lack of differentiation and of keratinization, mitotic rate, and nuclear polymorphism.…”

“…A proliferation score was determined by means of immunohistochemistry for Ki67 (MIB-1 antigen) as previously described. [3] In brief, digital images from several randomly chosen regions of each tumor were reviewed and 600–800 cells were counted, each. The percentage of positive cells was determined and resulted in the following scores: Score 0 was defined as 0–4% positive cells, score 1 as 5–19%, score 2 as 20–59%, and score 3 as more than 60% positive cells.…”

“…[2, 3, 16] In prior publications of our group, an accelerated external beam radiation therapy protocol applied to a small group of cats with nasal planum and periocular squamous cell carcinomas was observed to lead to better responses in cases with high Ki67 reactivity, i.e. faster proliferating.…”

“…faster proliferating. [2, 3, 16] With these earlier findings in mind, this retrospective, bi-institutional case series was compiled to assess the effectiveness of the previously published 10 × 4.8 Gy accelerated radiation therapy protocol in a larger group of cats with macroscopic cSCC of the nasal planum, and to evaluate tumor and treatment variables associated with local control and survival. Our hypothesis was that the accelerated hypofractionated radiation therapy protocol would result in a clinically acceptable acute and late toxicity profile and provide a long disease free interval (DFI) and overall survival (OS).…”