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

To determine the cut-off values of Ki-67 labeling index (LI) in the histological grading of follicular lymphoma (FL). 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. 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 test (<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, <0.01, 95% for 0.982-0.998). According to the analysis of four lattice diagnostic tests, Ki-67 LI >40% was an important factor (χ=230.733, <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 (=0.836, <0.01) was observed. 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.