The chronic lymphocytic leukemias and chronic myeloproliferative disorders are characterized by gradually increasing numbers of mature cells in the bone marrow, usually involving the peripheral blood and other organs.

Although none are rapidly fatal, hence the term chronic, they are difficult to classify because of their varied, but often overlapping morphologic and clinical characteristics. It is increasingly important to accurately classify these disorders as new chemotheraputic agents and cytokine therapies are developed.