Investigating the tumour microenvironment of CLL and Lymphoma The tumour micoenvironment of CLL and related lymphomas consists of multiple non-neoplastic elements including both adaptive and innate immune cells, stromal cells, blood vessels and extracellular matrix. Work to date indicates a supportive pro-tumoural role of CD4+ T cells as exemplified by the presence of a significant infiltrate of activated CD4+ T cells in tissue biopsies. Clinically relevant prognostic markers (for example, CD38 expression) can be influenced by the microenvironment. The microenvironment can also influence expression of enzymes such as activation induced deaminase (AID) thus linking the microenvironment with genomic instability. Ongoing work is continuing to explore how pro-tumoral elements support tumour progression.