Assessment of Ki-67 expression in Phyllodes tumor of breast: An Indian study

Abstract

Phyllodes tumor (PT) accounts for 0.3-1% of all breast tumors and classified into benign (BP), borderline (BLP) and malignant (MP). However, grading system is somewhat subjective and diagnosis remains challenging. Ancillary techniques may help in classification and prognostication of the tumor.Evaluation of the proliferative activity by Ki-67 index in Indian scenario.50 PTs received from January 2014 to December 2018 were graded using WHO criteria 2019. Ki-67 labelling index (LI) was calculated and graded 1+ (1-35%), 2+ (35-70%), 3+ (70-100%). Relevant statistical analysis was applied. P value of <0.05 was considered significant.70% (35) were BP, 26% (13) BLP and 4% (2) MP. Infiltrative margin, increased stromal cellularity, overgrowth, nuclear atypia and mitotic index were significantly associated with higher grade (P<0.000). The proportion of Ki-67 positive stromal cells in MP (mean76%) was higher than in BLP (mean 56.2%) and BP (mean 23.1%). Increasing Ki-67 index was significantly associated with infiltrative margin, presence of stromal overgrowth, increasing stromal cellularity, nuclear atypia, mitotic index and histological grade (P<0.000). Ki-67 statistically distinguished BP from BLP and MP (P<0.000, P<0.001 respectively), but not between BLP and MP (P<0.329). As a prognostic feature, high Ki-67 index expression did not predict local recurrence and due to fewer recurrent cases, the statistical correlation with any parameter could not be done.Histopathologic characteristics correlated with Ki-67 index. However, it was uncertain whether Ki-67 could provide independent prognostic information beyond histopathological typing. Continued follow-up with greater number of significant episodes may yield more informative correlations.