Pathophysiology
Summary
Lymphoid neoplasms, including conditions such as ALL (acute lymphoblastic leukemia/lymphoma) and CLL, have two main manifestations. They can present as leukemia where neoplastic lymphoid cells begin in the bone marrow and move to the peripheral circulation and lymphoma where these cells aggregate into tumor formations in lymphoid organs like the lymph nodes or the spleen. Histologically, lymphoblasts are distinguished by a large nucleus and minimal cytoplasm. Lymphoblasts are positive for periodic acid-Schiff (PAS) and terminal deoxynucleotidyl transferase (TdT).
Acute lymphoblastic leukemia/lymphoma (ALL) emerges from the uncontrolled growth of lymphoblasts in the bone marrow or lymphoid tissues and has a rapid onset and progression.. ALL can be either B-cell or T-cell in origin and is the most common cancer in children. Symptoms common to both types of ALL include functional pancytopenia, easy bruising, fever, hepatosplenomegaly, bone pain, & increased bleeding risk. ALL uniquely metastasizes to the CNS & testicles. Diagnosis of ALL requires an > 20% blast cells in the bone marrow. Down syndrome increases the risk of ALL.
B-cell ALL arises from a mutated pre-B cell in the bone marrow and us the most common type of ALL. Pre-B lymphoblasts show positivity for CD10, CD19, & CD20. T-cell ALL originates from a mutated pre T-cell in the thymus and is most prevalent in males 15-20 years old. T-cell ALL typically presents with an anterior mediastinal mass and lymphadenopathy, especially in the cervical, supraclavicular, and axillary areas, causing symptoms like superior vena cava syndrome, stridor, dyspnea, and dysphagia. Pre T lymphoblasts express markers like CD2, CD3, CD4, CD5, CD7, & CD8.
Chronic lymphocytic leukemia (CLL) results from the excessive growth of mature B lymphocytes in the bone marrow, is more prevalent in the elderly, and has a slow onset and progression. The neoplastic B cells prominently overexpress the proto-oncogene BCL2, enhancing their survival by preventing apoptosis. While CLL cells exhibit B-cell markers like CD19, they also uniquely express the T-cell marker, CD5.
In the diagnosis of CLL, leukocytosis consists mainly of B-cells. ‘Smudge cells’ may be observed on peripheral smear from the rupture of the fragile tumor cells during preparation. CLL manifests as lymphadenopathy, hepatosplenomegaly, hypogammaglobulinemia, and increased risk of bacterial infections. Abnormal CLL B-cells may generate autoantibodies against RBCs and platelets, inducing autoimmune hemolysis and thrombocytopenia. Consequently, CLL might display as functional pancytopenia despite evident leukocytosis or as small lymphocytic lymphoma (SLL) with dense small B-cells in lymphoid tissues.
Adult T-cell leukemia (ATL) commonly occurs in older adults due to human T-lymphotropic virus type 1 (HTLV-1) infection, resulting in excessive growth of CD4+ helper T cells. As TdT is only present in lymphoblasts, ATL cells lack this marker. Clinically, ATL leads to red plaques & papules on the skin, as well as lytic bone lesions that can induce hypercalcemia.
Hairy cell leukemia (HCL), a B-cell chronic lymphoid leukemia, mainly affects middle-aged men. Diagnostically, cells are Tartrate-Resistant Acid Phosphatase (TRAP) positive. Clinically, it causes significant splenomegaly from reticuloendothelial system infiltration. Bone marrow fibrosis due to HCL results in pancytopenia and a "dry tap" during biopsy. HCL is characterized by distinct clinical, histological, and biochemical markers.
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FAQs
Lymphoid neoplasms, such as acute lymphoblastic leukemia (ALL) and chronic lymphocytic leukemia (CLL), can present differently based on their origin and progression. ALL is characterized by the rapid proliferation of immature B and T-lymphocyte precursors, leading to symptoms like bone pain, fever, easy bruising, and bleeding. It is most common in children. In contrast, CLL involves the abnormal growth of mature B lymphocytes in the bone marrow and typically presents in older adults. CLL patients may experience lymphadenopathy, "smudge cells" on peripheral smears, and hypogammaglobulinemia, which can lead to bacterial infections.
ALL, which can be of B-cell or T-cell origin, manifests with a variety of symptoms including functional pancytopenia, easy bruising or bleeding, fever, and leukocytosis. Patients may also experience hepatosplenomegaly, lymphadenopathy, and bone pain. Additionally, ALL has a propensity to spread to the central nervous system, causing headaches, and to the testicles, resulting in a testicular mass.
Adult T-Cell Leukemia predominantly affects older adults and is caused by the human T-lymphotropic virus type 1 (HTLV-1), a retrovirus. This leukemia leads to the uncontrolled growth of mature CD4+ helper T cells. Symptoms can include red skin plaques and papules due to skin infiltration by leukemic cells. Other manifestations include lytic bone lesions, which can result in hypercalcemia.
Chronic lymphocytic leukemia (CLL) arises from the abnormal proliferation of mature B lymphocytes in the bone marrow. Typically presenting in older adults, CLL follows a slow, indolent course. Key features of CLL include leukocytosis, the presence of ‘smudge cells’ on peripheral smear, as well as lymphadenopathy and hepatosplenomegaly. A notable complication of CLL is hypogammaglobulinemia, which can predispose to recurrent bacterial infections.
Hairy cell leukemia is a unique B-cell neoplasm that predominantly affects middle-aged men. A hallmark of this leukemia is its positive staining for tartrate-resistant acid phosphatase (TRAP). Clinically, it can lead to massive splenomegaly due to infiltration of the reticuloendothelial system. Patients often present with bone marrow fibrosis and pancytopenia. A characteristic ‘dry tap’ during a bone marrow biopsy, where the biopsy fails to produce contents, is also indicative of hairy cell leukemia.
