[Cut-off value of Ki-67 labeling index in the pathologic grading of follicular lymphoma]

Objective: To determine the cut-off values of Ki-67 labeling index (LI) in the histological grading of follicular lymphoma (FL). Methods: Clinicopathological data of 350 FL patients diagnosed at Beijing Friendship Hospital from June 2014 to January 2016 were analyzed retrospectively by quantitative evaluation and statistical analysis of Ki-67 LI. Results: Of the 350 patients with FL, the male and female ratio was 1.1 and the average age was (50.2±14.0) years with a median age of 51 years (range 4 to 82 years). The tumors were graded as grade Ⅰ-Ⅱ in 215 cases (61.4%), grade Ⅲ A in 105 cases (30.0%), and grade Ⅲ B in 30 cases (8.6%). The average Ki-67 values were (22.8%±8.3%) for the FL low (grade Ⅰ-Ⅱ) and (50.4%±10.7%) for high grade (Ⅲ A and Ⅲ B) and were statistically significant by Mann Whitney U test (P<0.01). Receiver operated characteristic curve analysis showed that the best diagnostic cut-off value of low grade FL was 35% (sensitivity of 96.3% and specificity of 93.3%) with the largest area under curve (AUC=0.990, P<0.01, 95%CI for 0.982-0.998). According to the analysis of four lattice diagnostic tests, Ki-67 LI >40% was an important factor (χ2=230.733, P<0.01) in predicting high grade FL. When the cut-off value of Ki-67 LI was set at 40%, high grade LF could be diagnosed with the greatest sensitivity (98.1%) and specificity (87.7%). Moreover, a significant correlation between the Ki-67 LI and the pathological grade of FL (r=0.836, P<0.01) was observed. Conclusions: Ki-67 LI of below a cut-off value of 35% is a reliable indicator of low grade FL.Ki-67 over 40% is consistent with high grade FL. These Ki-67 cut-off values may serveas an important auxiliary indicator in the grading of FL.