Blood cancer is a diverse group of diseases that result from the neoplastic proliferation of a malignant blood cell in the hematopoietic system. The clinical presentation of blood cancer is variable and depends largely on the location and severity of the disease.
Classification of blood cancer
Blood cancers are classified as myeloid (related to the bone marrow) or lymphoid (related to the tissues that produce lymphocytes and antibodies) depending on the hematopoietic lineage in which an abnormality occurred; they can also be classified into one of the following groups:
Conceptual image illustrating the destruction of a leukaemia cell as a result of treatment.
Leukaemia is a cancer in which malignant hematopoietic cells are found in the bone marrow and peripheral blood. Leukaemia can be classified as myeloid or lymphoid, acute or chronic, depending on how quickly the disease breaks out. In acute leukaemia, there is an abnormal proliferation of blasts (poorly differentiated immature cells) and maturation arrest may occur. In contrast, in chronic leukaemia, there are no blasts as the malignant cells continue to mature during hematopoiesis.
Lymphomas affect the lymphoid lineage and are chronic malignancies. Malignant lymphoid cells usually accumulate in and are confined to the lymphoid organs, resulting in a lymphoid static tumour. When the affected lymphoid organ becomes so crowded with malignant cells that they accumulate there, the cells may invade organs outside the lymphoid tissue, such as the peripheral blood and bone marrow. Lymphomas are broadly classified as Hodgkin's lymphoma (HL) and non-Hodgkin's lymphoma (NHL), depending on whether the malignant tumour contains Reed-Sternberg cells (abnormal lymphocytes found only in HL ).
Myelodysplastic syndromes are myeloid malignancies in which immature myeloid progenitor cells accumulate in the bone marrow. As a result, these immature cells die before they can mature into effector cells. This leads to ineffective haemopoiesis and consequently to a reduction in red blood cells, white blood cells and platelets.
Conception image showing the secretion of excess immunoglobulin (M proteins) from the malignant plasma cells (myeloma cells) in multiple myeloma.
Multiple myeloma is a lymphoid malignancy in which there is an abnormal proliferation of malignant plasma cells. In a healthy state, plasma cells are required for the production of antibodies. In multiple myeloma, the malignant plasma cells oversynthesize and secrete excessive amounts of monoclonal immunoglobulins called paraproteins. In excessive concentrations in plasma, the paraproteins can cause severe tissue damage to a number of organs.
Myeloproliferative disorders are myeloid abnormalities in which there is an abnormal overproduction of myeloid cells in the bone marrow, usually causing erythrocytosis, thrombocytosis, neutrophilia, and basophilia. The major myeloproliferative disorders are CML, polycythaemia vera, myelofibrosis and essential thrombocythaemia.
Investigation of blood cancers
The role of a pathology laboratory is essential in the investigation of blood cancers. It is important to accurately diagnose malignancies because treatment strategies vary widely and an incorrect diagnosis can have a major impact on a patient's prognosis. There are many different tests and analytical techniques that can be used in the investigation of a suspected blood cancer, including the following:
A complete blood count (FBC) provides data on red blood cell, white blood cell, and platelet indices. These parameters are critical because they indicate the number of each cell line and help determine bone marrow involvement. In some cases, the results of the blood count are one of the first indications of suspected blood cancer, and the analysis of the blood count may lead to requesting further tests.
Morphological analysis of blood by examining a blood film under a microscope.
Morphological examination of peripheral blood and/or bone marrow helps to identify the shape, size, characteristics, cellular inclusions and maturity of blood cells. Certain morphologic features are clearly associated with specific types of blood cancers. Therefore, analysis of morphology is crucial in making a diagnosis or determining further investigations.
Immunophenotyping analyzes the expression of antigenic markers expressed on the cell surface. These markers are referred to as clusters of differentiation (CD). Specific markers associated with each cell lineage allow the identification of cell populations. In healthy individuals, certain CD markers should be present. However, in malignancies, there may be loss of expression, overexpression, and aberrant expression of certain markers that should not be present in a healthy individual. By comparing the results to normal expected expression, healthy and malignant cell populations can be distinguished.
Cytogenetics examines cells at the molecular level because some blood cancers are caused by a chromosomal mutation. By analyzing the carotype and chromosomal structure of a patient, genetic mutations can be identified.
Histological processing of a tissue biopsy
Histological examination of a biopsy (e.g., of a lymph node) can provide information about the architecture of the tissue and the type of cells present. This helps to determine the presence and/or spread of malignant disease.
Due to the heterogeneous nature of blood cancers, a multidisciplinary laboratory approach is often required for diagnosis. Therefore, to aid in the diagnosis, all laboratory results must be interpreted in conjunction with the clinical presentation.
Innovations and advances in the field of blood cancers are making rapid progress to reduce the prevalence of such diseases and improve the prognosis for those affected.