Role of Ki 67 Labelling Index as an Adjunct to Histopathological Diagnosis for Grading of CNS Tumours

Abstract

BACKGROUND The Central Nervous System tumours are unique as they arise from specialized tissue. CNS tumours constitute a wide range of neoplasm that differs in their location, age distribution, extent of invasiveness, morphological features and tendency for progression. We wanted to evaluate the traditional morphological data with knowledge on the prognostication marker Ki 67 antibody in evaluating tumour grade and prognosis of CNS neoplasm. METHODS This is a cross section study carried out between March 2015 and September 2016 in histopathology department of Dhiraj Hospital on 50 cases of CNS tumours. Immunolabelling of all biopsies was done by horse radish peroxidase technique using rabbit monoclonal antibody to Ki 67 (clone SP 6) (Thermo Scientific, USA). Ki 67 immune positive labelling index was obtained for each tumour and correlated with mitotic labelling index obtained by conventional morphological grading as per WHO 2007 classification. RESULTS In our study of CNS tumours, all age groups were studied. The mean Ki 67 labelling index (LI) values +/-SD for WHO Grade I tumours were- meningiomas (10) 3.85 (+/1.97) %, schwannoma (3) -3.0 (+/-2.97) %, pituitary adenoma (1) 0.6, craniopharyngioma (1) -1.1% and ependymoma (6) 2.62 (+/-0.60) %. WHO Grade II tumours- atypical angiomatous meningioma (1) -2%, atypical mucinous meningioma (2) -6.15 (+/-1.06) %, gemistocytic astrocytoma (1) -12; pleomorphic xanthoastrocytoma (2) -4.3 (+/-0.99) %, astrocytoma grade ii (2) -3.3 (+/-0.71) %, oligodendroglioma grade ii (4) - 3.9 (+/-0.88) %. WHO grade III tumours- anaplastic astrocytomas (5) -6.82 (+/-2.17) %, anaplastic oligoastrocytoma grade iii (1) -10.8 %. who grade iv-glioblastomas (7) -18.44 (+/-3.97) %; medulloblastomas (1) 20%, metastatic tumour (3) -36 (+/- 22.16) %. In our study, the mean Ki 67 LI (± SD) values for grade II, III and IV glioma is as follows: 4.76 (+/-2.83) %, 7.48 (+/-2.53) % and 18.44 (3.97) % respectively. CONCLUSIONS This study shows that Ki 67 LI serves as an essential clinical prognostic proliferation marker of particular importance in cases with lower grade histology of Grade II & Grade III astrocytomas, Grade II & Grade III oligodendrogliomas. Ki 67 LI is important in determining benign, atypical and malignant meningiomas, non-invasive and invasive pituitary adenomas.