Primary central nervous system lymphoma (PCNSL) is a rare cancer with a generally poor outcome and with very limited therapeutic choices resulting in a short patient survival (the median overall survival ranges from 2 to 4 years). Despite intensive research activities, our understanding of the disease remains obscure; moreover, most of the data has emerged from relatively small studies. In this project we will investigate the origin of tumour cells in a relatively large cohort of PCNSL and correlate the results to clinical data and the frequency of mutations of different genes involved in development of PCNSL. We will use different modern molecular and immunohistochemical techniques. Our research will lead to better understanding of PCNSL, and ultimately will allow us to offer novel prognostic biomarkers and potential therapeutic targets to the patients.