Bcl-2 Expression Inversely Correlates with Tumour Cell Differentiation in Medulloblastoma

Medulloblastoma (MB) is a cerebellar primitive neuroectodermal tumour that occurs predominantly in childhood. It can be mainly divided into classical and desmoplastic tumours, but differential diagnosis is often difficult. Patients' prognosis is poor and neuropathological markers that reliably predict outcome are still missing. In a series of 104 MBs including 80 tumours of the classical and 24 tumours of the desmoplastic variant we studied the number of apoptotic figures and the expression of the proto-oncogene bcl-2, an anti-apoptotic protein known to affect tumour cell proliferation. We observed a strong correlation between the expression of bcl-2 with patients' age (P < 0.001) as well as with the desmoplastic subtype (P < 0.001). Here, protein expression was found to be restricted to internodular, less differentiated, highly proliferative areas. In classical MB, bcl-2 was detected only in 23% of cases and was highly inversely correlated with the expression of synaptophysin (P < 0.001) indicating that bcl-2 is predominantly expressed by undifferentiated classical MB. With regard to prognosis the expression of bcl-2 tended to correlate with poor outcome in classical MB but not in desmoplastic MB, although not to a statistically significant extension (P = 0.06). On the other hand, a high number of apoptotic figures in the tumour tissue was found to indicate poor prognosis independent of the histological subtype (P < 0.05).