Ki-67: A prognostic factor for low-grade glioma?

Abstract Purpose: Immunohistochemical techniques were used to detect the expression of Ki-67, a nuclear proliferation marker, in 180 low-grade glioma tumor specimens to determine whether Ki-67 is a prognostic predictor of survival or tumor recurrence. Methods and Materials: A clinical database of 180 low-grade glioma patients (35 children aged ≤18 years and 145 adults) was compiled. Eighty patients had received postoperative radiotherapy (RT) and 100 patients had had RT deferred until the time of tumor progression/recurrence. Ki-67 indexes were evaluated retrospectively on tumor specimens from these patients using a semiautomated computer analysis technique. Ten observations were averaged per patient. The maximal Ki-67 value was recorded. Results: The correlation between the Ki-67 index and survival was much higher for the averaged Ki-67 value than for the maximal value. Of the tumor specimens, 29% had a negative Ki-67 index (i.e., zero Ki-67 positive cells) and 7.7% had an average Ki-67 index of ≥5%. An average Ki-67 value of ≥5% was prognostically significant for reduced cause-specific survival (CSS, p = 0.05) and a Ki-67 level ≥10% was strongly significant of a poor survival outcome ( p = 0.009). Ki-67 was not prognostically significant for progression-free survival. Other prognostically significant factors for CSS included age ( p = 0.05), Karnofsky performance status ( p = 0.0001), radiation dose ( p = 0.02), extent of surgical resection (biopsy vs. others, p = 0.004), and timing of radiation ( p = 0.0005). Ki-67 did not remain an independent statistically significant factor for CSS on multivariate analysis. Age and Ki-67 positivity (both maximal and average values) directly correlated (i.e., advancing age was associated with a higher Ki-67 index). When the patient group was further subdivided by age and timing of RT (postoperative vs. deferred), the prognostic significance of Ki-67 for CSS was lost. Within the deferred RT subgroup, a maximal Ki-67 >2% was associated with a worsened CSS. Within the pediatric population, Ki-67-negative patients had a 5-year CSS and progression-free survival of 100%. The 5-year CSS and progression-free survival declined significantly to 84% and 67% for patients with tumors demonstrating any degree of Ki-67 positivity ( p = 0.005 and p = 0.006, respectively). Conclusion: Ki-67 is a useful predictor of CSS in low-grade gliomas; however, it is not independent of other prognostic factors, particularly age. Although Ki-67 was not helpful in predicting which adult patients were likely to benefit from postoperative RT, the results of the present study indicate a possible utility in the selection of pediatric patients for RT and in the selection of poorer prognosis patients for clinical trials.