hematology and oncology
Overview of Leukemia
Classification of Leukemia
The current approach to classifying leukemia is based on the 2016 World Health Organization (WHO) system (classification for hematopoietic neoplasms). The WHO classification is based on a combination of clinical features and morphology, immunophenotype, and genetic factors. Other less commonly used classification systems include the French-American-British (FAB) system, which is based on the morphology of the abnormal leukocytes. Leukemias are commonly also categorized as Acute or chronic: Based on the percentage of blasts or leukemia cells in bone marrow or blood Myeloid or lymphoid: Based on the predominant lineage of the malignant cells The four most common leukemias and their distinguishing features are summarized in the table. For 2023, the American Cancer Society estimates the distribution of new cases in the United States by leukemia type as follows ( General reference ): Acute Myeloid Leukemia (AML) (AML): 34% Acute Lymphoblastic Leukemia (ALL) (ALL): 11% Chronic Myeloid Leukemia (CML) (CML): 15% Chronic Lymphocytic Leukemia (CLL) (CLL): 31% Other leukemias: 8% Acute leukemias consist of predominantly immature, poorly differentiated cells (usually blast forms). Acute leukemias are divided into Acute Lymphoblastic Leukemia (ALL) (ALL) Acute Myeloid Leukemia (AML) (AML) Chronic leukemias have more mature cells than do acute leukemias. They usually manifest as leukocytosis with or without cytopenias in an otherwise asymptomatic person. Findings and management differ significantly between Chronic Lymphocytic Leukemia (CLL) (CLL) Chronic Myeloid Leukemia (CML) (CML) Myelodysplastic Syndrome (MDS) are a group of clonal hematopoietic stem cell disorders unified by the presence of distinct mutations of hematopoietic stem cells. They involve progressive bone marrow failure but with an insufficient proportion of blast cells ( A leukemoid reaction is a neutrophil count > 50,000/mcL (> 50 × 109/L) not caused by malignant transformation of a hematopoietic stem cell. It can result from a variety of causes, particularly other cancers or systemic infection. Usually the cause is apparent, but apparent benign neutrophilia can be mimicked by chronic neutrophilic leukemia or chronic myeloid leukemia. 1. American Cancer Society: Cancer Facts and Statistics.https://www.cancer.org/research/cancer-facts-statistics.html 