Leukemias are categorized based on white blood cell type affected (lymphocytes vs myeloid cells) and whether the disease is developing very quickly (acute) or slowly over time (chronic).
Hairy cell leukemia (HCL) is a rare, chronic lymphocytic cancer in which the bone marrow overproduces B lymphocytes. These B cells have an abnormal structure under microscope and are hairy in appearance. As the disease progresses fewer healthy WBCs, RBCs, and platelets are produced. HCL affects more men than women, and it develops most frequently in middle-aged or older adults. Patients with this disorder may remain in remission for years as the affected cells may not all be eradicated. The specific cause of HCL is unclear, but like with other cancers it is likely due to the development of mutations that lead to uncontrolled proliferation of bone marrow stem cells.
Chronic lymphocytic leukemia (CLL) is a mature B cell neoplasm characterized by a progressive accumulation of monoclonal B lymphocytes that manifests primarily in the blood.
- Most common leukemia in adults within the US accounting for 25 to 30 percent.
- Male to female ratio around 1.3:1 to 1.7:1
- Mean age of diagnosis around 70 years of age
- Incidence much higher in Whites vs Blacks or Asians independent of geography indicating a strong genetic component rather than an environment cause to this disorder.
- Skin lesions (leukemia cutis) most commonly involve the face and can manifest as macules, papules, plaques, nodules, ulcers, or blisters
There are also several chronic myeloid leukemias such as chronic neutrophilic leukemia, chronic eosinophilic leukemia, and chronic myelogenous leukemia (CML) which are all categorized as myeloproliferative neoplasms.
In chronic neutrophilic leukemia there is an overproduction of neutrophils detectable within the blood of the patient and can stay the same for many years or develop into acute leukemia. The excess neutrophils can lead to hepatosplenomegaly.
Chronic eosinophilic leukemia is characterized by an overproduction of eosinophils that can be seen in bone marrow and blood in addition to many other tissues throughout the body. This leukemia can also stay the same for many years or progress to an acute leukemia.
CML is characterized by dysregulated proliferation of mature and maturing granulocytes (neutrophils, basophils, and eosinophils) with fairly normal differentiation. Proliferation of all granulocytes is increased, but neutrophils in particular are elevated the most. Left untreated, CML has a three or two step course of disease progression as it evolves from a chronic phase to an accelerated phase and then to a terminal blast crisis. In the two step clinical course the disease can progress from chronic phase directly to the blast phase, especially when the blast phase is lymphoid but myeloid blast cells can also proliferate in an uncontrolled manner. About 85% of patients that are diagnosed with CML are in the chronic phase. In the accelerated phase of the disease neutrophil differentiation becomes increasingly impaired and the elevation in leukocyte counts are becoming increasingly difficult to control with treatment.
CML is caused by the fusion of two genes: BCR (Ch 22) and ABL1 (Ch 9) as a result of a reciprocal translocation t(9;22)(q34;q11) leading to the production of the BCR-ABL1 fusion protein. The abnormal chromosome 22 is known as the Philadelphia chromosome. The ABL1 portion of the fusion protein contains tyrosine kinase catalytic activity that is upregulated due to the BCR portion of the protein leading to the pathology associated with CML.