BackgroundGiant cell tumor is an infrequent and unpredictable bony lesion. Although numerous attempts have been made to predict the behaviour of GCT, there are no definite biological or histological parameters to determine the prognosis or aggressiveness of this lesionMaterials and methodsWe analyzed Ki 67 immuno-histochemistry of 31 consecutive cases staged III giant cell tumor to determine the clinico-pathological correlation. There were 19 male patients compare to 12 females. The mean age was 33.8 years ranged from 18 to 59 years. Five cases presented with local recurrence prior to wide resection and one case had multiple recurrences there after. Six cases had pulmonary metastases. Expression of Ki 67 antigen was evaluated by immuno-histochemical staining techniques using the avidin-biotin perioxidase complex method using an LSAB2 kit (Dako, Glostrup, Denmark). The primary antibody used in this study was Ki-67 (MIB-I clone, dilution 1:25; Dako).ResultsThe mean value of Ki-67 index obtained as a percentage of 1000 background cells was 8.15 (ranged 1.00 - 20.0). The median Ki 67 index was 7.5 with standard deviation of 5.12. The Ki 67 index of recurrence tumor was 4.323 compared to 6.05 without recurrence and was not statistically significant (mean difference of 0.865 with p value in independent t test of 0.736). The Ki 67 index was also not statistically significant in the presence of pulmonary metastases with the mean value of metastases group of 6.681 compared to 2.890 without metastases (mean difference of 1.895 with p value in independent t test of 0.424).ConclusionKi 67 index is not use-full prognostic marker for aggressive type of giant cell tumor of the bone.