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Although hematological malignancies are a form of cancer, they are generally treated by specialists in hematology, although in many hospitals oncology specialists also manage these diseases. ("Hematology/Oncology" is a single subspecialty of Internal Medicine; there are also surgical and radiation oncologists.)

Hematological malignancies are the types of cancer that affect blood, bone marrow and lymph nodes. As the three are intimately connected through the immune system, a disease affecting one of the three will often affect the others as well: although lymphoma is technically a disease of the lymph nodes, it often spreads to the bone marrow, affecting the blood and occasionally producing a paraprotein.

Chromosomal translocations are a common cause of these diseases, while this is uncommon in solid tumors. This leads to a different approach in diagnosis and treatment of hematological malignancies.

The hematological malignancies include:

• Leukemia:
  • Acute lymphoblastic leukemia (ALL)
  • Acute myelogenous leukemia (AML)
  • Chronic myelogenous leukemia (CML)
  • Chronic lymphocytic leukemia (CLL)
  • Hairy cell leukemia
• Lymphoma:
  • Hodgkin's disease (four subtypes)
  • Non-Hodgkin lymphoma (many subtypes)
• Multiple myeloma

Related disorders, which are generally not called "cancer":

• Myelodysplastic syndrome (MDS) - can culminate in AML
• Myelofibrosis
• Myeloproliferative disease:
  • Polycythemia vera (PV, PCV or occasionally polycythemia rubra vera - PRV)
  • Essential thrombocytosis (ET)
• Amyloid due to light-chain disease

For the analysis of a suspected hematological malignancy, a complete blood count and blood film are essential, as malignant cells can show in characteristic ways on light microscopy. When there is lymphadenopathy, a biopsy from a lymph node is generally undertaken surgically. In general, a bone marrow biopsy is part of the "work up" for the analysis of these diseases. All specimens are examined microscopically to determine the nature of the malignancy. A number of these diseases can now be classified by cytogenetics (AML, CML) or immunophenotyping (lymphoma, myeloma, CLL) of the malignant cells.

Treatment can occasionally consist of "watchful waiting" (e.g. in CLL) or symptomatic treatment (e.g. blood transfusions in MDS). The more aggressive forms of disease require treatment with chemotherapy, radiotherapy, immunotherapy and - in some cases - a bone marrow transplant.

If treatment has been successful ("complete" or "partial remission"), a patient is generally followed up at regular intervals to detect recurrence and monitor for "secondary malignancy" (an uncommon side-effect of some chemotherapy and radiotherapy regimens - the appearance of another form of cancer). In the follow-up, which should be done at pre-determined regular intervals, general anamnesis is combined with complete blood count and determination of lactate dehydrogenase or thymidine kinase in serum.