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Classification of Hemoblastoses

For medical students2 min readUpdated 2026-10-10

Hemoblastoses represent a broad group of neoplastic disorders affecting the hematopoietic tissue. In pathophysiology, they are classified based on two fundamental criteria: the peculiarities of their clinical course and the specifics of the cellular substrate, dividing all pathologies into acute and chronic forms.

Classification criteriaClinical course and cellular substrate of the tumor
Acute formsCharacterized by an immature blast cell substrate
Chronic formsRepresented by relatively differentiated cells
Pediatric incidenceAccount for approximately 30% of all malignancies in children
Blast crisisTransformation of a chronic process into an acute course

Nomenclature Principles and Base Criteria

The key factor determining whether a hemoblastosis belongs to a particular group is the degree of maturity of the cells comprising the tumor.

It is important to understand that the terms "acute" and "chronic" in this context reflect not so much the speed of symptom development as the morphological substrate and the degree of tumor cell differentiation.

Acute Forms of Hemoblastoses

The morphological substrate of acute leukemias is always blast tumor cells. These are extremely aggressive conditions. If left without specialized treatment, the disease invariably leads to death within a few weeks or months. However, with appropriate and timely therapy, the prognosis changes drastically and can be quite favorable.

Based on the cellular composition, the following variants of acute hemoblastoses are distinguished:

These diseases are of particular concern in pediatric practice. Acute leukemias constitute about 30% of all malignant tumors diagnosed in children. The absolute leader in frequency is acute lymphoblastic leukemia (ALL), accounting for approximately 24% of cases, making it the most common pediatric malignancy. The peak incidence for this form is observed in toddlers aged 2–3 years. Acute myeloid leukemia accounts for a significantly smaller share in children—around 6%.

Modern medicine demonstrates high treatment efficacy: in recent years, physicians have achieved sustained and long-term remission in nearly 90% of clinical cases of acute lymphoblastic leukemia.

Chronic Forms and Their Transformation

In contrast to acute processes, the cellular substrate of chronic hemoblastoses consists of relatively differentiated cells of the hematopoietic tissue.

Classification of chronic forms is also based on the predominant cell type. There are five main variants:

  1. Chronic lymphocytic leukemia (CLL). Hairy cell leukemia is traditionally included in this same group.
  2. Chronic myeloid leukemia (CML).
  3. Chronic myelomonocytic leukemia.
  4. Erythrocytic hemoblastosis. In clinical practice, this condition is frequently referred to as polycythemia vera or Vaquez disease.
  5. Megakaryocytic hemoblastosis.

A critically important aspect of the pathophysiology of chronic hemoblastoses is their ability to progress and alter their cellular composition. Chronic forms frequently transform into their acute counterparts. This ominous process, accompanied by a sharp deterioration in the patient's condition, is termed acute transformation of chronic hemoblastosis, or blast crisis.

Mnemonic

To easily remember the terminology: if a disease name contains the root "-blast" (e.g., myeloblastic), it is always an acute hemoblastosis. If it contains "-cytic" (myelocytic), you are dealing with a chronic form.

Frequently asked questions

What are the characteristic peripheral blood (hemogram) findings in acute leukemias?

Characteristic peripheral blood changes in acute leukemias include the appearance of blast cells, suppression of normal hematopoiesis, and specific phenomena. Key findings include:

  • Hiatus leukaemicus (hiatus leukaemicus) — the presence of blast cells and mature forms alongside a complete absence of intermediate maturing cells, which is pathognomonic for acute myeloid leukemia.
  • Leukemization — the release of immature and blast tumor cells into the bloodstream.
  • Cytopenia — the development of anemia, thrombocytopenia, and neutropenia due to the displacement of normal hematopoietic lineages by the neoplastic blast clone.
What specific cytogenetic markers are characteristic of chronic myeloid leukemia?

The key cytogenetic marker of chronic myeloid leukemia is the Philadelphia chromosome.

  • Philadelphia chromosome (Ph chromosome) — an abnormal 22nd chromosome, the presence of which is the primary diagnostic hallmark of this pathology.
  • Chimeric gene (BCR-ABL) — the gene associated with this mutation, which encodes a specific protein.

The consequence of this abnormality is enhanced tyrosine kinase enzyme activity, leading to stimulated cellular proliferation and delayed terminal differentiation.

What is the main criterion for dividing hemoblastoses into acute and chronic?

The primary criterion is the cellular substrate of the tumor. Acute hemoblastoses consist of immature blast cells, whereas chronic forms are represented by relatively differentiated, more mature cells of the hematopoietic tissue.

What is the prognosis for a patient with acute hemoblastosis?

Without medical intervention, the prognosis is extremely unfavorable, resulting in death within a few weeks or months. However, with correct and timely therapy, the prognosis can become favorable. For instance, long-term remission in acute lymphoblastic leukemia is achieved today in nearly 90% of cases.

How common are hemoblastoses in childhood?

Acute leukemias account for about 30% of all malignant tumors in children. The most common is acute lymphoblastic leukemia (about 24%), with a peak incidence at 2–3 years of age. Acute myeloid leukemia is less common, occurring in approximately 6% of cases.

What does the term "blast crisis" mean?

A blast crisis is the acute progression of a chronic hemoblastosis, during which the disease transforms into an acute form. During this period, the pool of immature blast cells in the hematopoietic tissue begins to expand rapidly.

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