Pathogenesis and Cellular Properties
Lymphoid cells constitute a highly heterogeneous population that varies in immunophenotypic and functional characteristics. The capacity for neoplastic transformation is retained at virtually every stage of cellular differentiation. This accounts for the immense diversity of lymphoproliferative disorder forms.
Properties of malignant lymphoid cells include:
- Presence of normal counterparts: in most cases, tumor cells closely correspond to a specific maturation stage of normal lymphocytes.
- Monoclonality: the basis of tumor growth.
- Genetic rearrangement: during the differentiation of T and B lymphocytes, a characteristic rearrangement of the genes encoding their receptors occurs. These alterations are preserved in the tumor clone.
Differential Diagnosis: Clonality
Normally, each lymphocyte acquires a unique antigen receptor. During tumor progression, this specific receptor is repeatedly reproduced across all daughter cells. As a result, a monoclonal population is formed.
Detecting monoclonality is of critical diagnostic importance. This feature allows the pathologist to reliably distinguish true neoplasia from reactive conditions or polyclonal leukemoid reactions.
Primary Localization and Biological Unity
Based on the site of primary origin, tumors are divided into two broad groups:
- Lymphoid leukemias — transformation primarily occurs in the bone marrow.
- Lymphomas (lymphosarcomas) — primarily have extramedullary localization (lymph nodes, spleen, skin, mucosa-associated lymphoid tissue).
Modern medicine recognizes the concept of biological unity. It proves the relationship between leukemias and lymphomas of the same lineage regardless of where they originated (in the bone marrow or an extranodal site).
For example, acute lymphoblastic leukemia and lymphoblastic lymphoma share histogenetic similarities and common genetic aberrations, although they are not clinically fully identical. The same applies to the pair «chronic B-cell lymphocytic leukemia — small lymphocytic lymphoma». The boundary between them blurs during the leukemic phase, when the lymphoma infiltrates the bone marrow and spills into the blood.
General Characteristics and Classification of Lymphomas
Lymphomas are malignant monoclonal neoplasms derived from transformed cells at various levels of differentiation (before or after contact with the thymus, lymph nodes, or spleen). They can involve any organ containing lymphoid tissue.
The disease often begins in lymph nodes, progressing to involve new groups, the spleen, liver, and bone marrow. Clinically, this manifests as prominent lymphadenopathy and splenomegaly. Without treatment, tumors tend to disseminate and metastasize, carrying an unfavorable prognosis.
Based on cytogenesis, they are classified into:
- B-cell neoplasms.
- T- and NK-cell neoplasms (e.g., angioimmunoblastic T-cell lymphoma, anaplastic large cell lymphoma).
- Hodgkin lymphoma (Hodgkin disease).
To verify the diagnosis according to the WHO classification, it is necessary to establish lineage, degree of differentiation, stage of dissemination, and molecular-genetic alterations.
Variants of Hodgkin Lymphoma
Hodgkin lymphoma is classified into several morphological variants:
- Nodular lymphocyte-predominant Hodgkin lymphoma.
- Classical variants: lymphocyte-rich, nodular sclerosis, mixed cellularity, and lymphocyte depletion.