Ki-67 as a Prognostic Factor in Feline Mammary Carcinoma

Abstract

Ki-67 is a nuclear protein and a proliferation marker frequently used in establishing the prognosis for breast cancer patients. To investigate the prognostic value of the Ki-67 proliferation index in female cats with mammary carcinoma, a prospective study was conducted with 96 animals. The Ki-67 index of primary tumors ( n = 96) was initially determined, and whenever possible, the Ki-67 index of regional lymph node metastasis ( n = 38) and distant metastasis ( n = 16) was also estimated. The optimal cutoff value for the Ki-67 index was determined by univariate and multivariate analysis. Ki-67 indices ≥14% were detected in 72.9% (70 of 96) of the tumors. Tumors with a Ki-67 index ≥14% were significantly associated with large size ( P = .022), poor differentiation ( P = .009), presence of necrotic areas ( P = .008), estrogen receptor-negative status ( P < .0001), fHER2-negative status ( P = .003), and shorter overall survival ( P = .012). Moreover, Ki-67 expression in the primary tumor was strongly and positively correlated with both regional metastasis ( P < .0001; r = 0.83) and distant metastasis ( P < .0001; r = 0.83), and was significantly higher in distant metastases when compared with the primary tumor ( P = .0009). A similar correlation was also observed between regional and distant metastasis ( P < .0001; r = 0.75). On the basis of the above results, the authors propose the adoption of the 14% value as the optimal cutoff for Ki-67 to identify tumors with high risk of disease progression.