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We describe a patient with a primary diffuse large B-cell lymphoma of the central nervous system who developed a localized testicular relapse after 8 years. Both tumours lacked HLA-DR expression, the relapse additionally lost HLA class I expression. Immunoglobulin heavy chain gene rearrangements were identical in both lymphomas with extensive and ongoing somatic hypermutations resulting in extensive idiotype modulation. We hypothesize that these immune sanctuaries initially provided a safe haven for the tumour cells. When the environment becomes more permissive for an anti-tumour response, the continuous idiotype modulation and progressive loss of HLA expression on the tumour cells facilitates further immune escape.