Tumors of the hematopoietic and lymphoid tissues (American English) or tumours of the haematopoietic and lymphoid malignancies (British English) are tumors that affect the blood, bone marrow, lymph, and lymphatic system. Because these tissues are all intimately connected through both the circulatory system and the immune system, a disease affecting one will often affect the others as well, making myeloproliferation and lymphoproliferation (and thus the leukemias and the lymphomas) closely related and often overlapping problems. [Source: Wikipedia 
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