Lymphoma – Top USMLE Diseases

Non-Hodgkin lymphomas (NHLs) are a diverse group of hematologic malignancies that are clonal proliferative disorders of mature or progenitor B cells, T cells, or natural killer (NK) cells. Most pediatric cases are aggressive and high-grade (but curable); in adults, low-grade subtypes are more common. Like Hodgkin lymphoma, which has distinct pathologic features and treatments, NHL often presents with constitutional signs of fever, night sweats, and weight loss. Clinical features include lymphadenopathy and hepatosplenomegaly, but some individuals present with extranodal involvement and abnormal lab findings. B-cell NHLs include diffuse large B-cell lymphoma, follicular lymphoma, Burkitt lymphoma, mantle cell lymphoma, and marginal zone lymphoma. T-cell NHLs include adult T-cell lymphoma and mycosis fungoides. Diagnosis is made by lymph node biopsy, bone marrow biopsy, or both. Management is with chemotherapy or targeted drugs. Radiation therapy is used in adults but not in children, and stem cell transplantation is used for patients with aggressive disease.

Extranodal marginal zone lymphoma (EMZL) of mucosa-associated lymphoid tissue (also called MALToma, MALT lymphoma, and pseudolymphoma) is a group of non-Hodgkin’s lymphomas that have historically been grouped together because they appear to arise from postgerminal center marginal zone B cells and share a similar immunophenotype. MALT lymphoma is thought to arise in the setting of chronic immune stimulation, which is usually due to bacterial, viral, or autoimmune stimuli. MALT lymphomas present with symptoms due to localized involvement of glandular epithelial tissues in the specific site where they develop. Diagnosis of MALT lymphoma is made by morphologic, immunophenotypic, and genetic analysis of biopsy samples. Helicobacter pylori–positive gastric MALT lymphoma is treated with H. pylori eradication therapy, and H. pylori–negative gastric MALT lymphoma is treated with radiation therapy. Nongastric MALT lymphoma is treated based on the involved area and extent of disease. MALT lymphoma patients have a good prognosis, with a median survival of > 10 years.

Lymphadenopathy is lymph node enlargement (> 1 cm) and is benign and self-limited in most patients. Etiologies include malignancy, infection, and autoimmune disorders, as well as iatrogenic causes such as the use of certain medications. Generalized lymphadenopathy often indicates underlying systemic disease. Diagnosis relies on a thorough medical history and physical examination, which usually identify the underlying cause. When the cause is unknown, a biopsy may be necessary. Management is directed at the underlying infection, malignancy, or other cause.

Chronic lymphocytic leukemia (CLL) is a hematologic malignancy characterized by excess production of monoclonal B lymphocytes in the peripheral blood. When the involvement is primarily nodal, the condition is called small lymphocytic lymphoma (SLL). The disease usually presents in older adults, with a median age of 70 years. Clinical presentation is often asymptomatic and diagnosis is made when abnormal lymphocytosis is seen on laboratory testing. Cytopenias can also be seen. The B cells are functionally incompetent lymphocytes and thus may result in recurrent infections. Treatment can vary from watchful waiting for early stages to chemotherapy for later stages. Median survival is around 10 years.

Acute myeloid leukemia (AML) is a hematologic malignancy characterized by the uncontrolled proliferation of myeloid precursor cells. Seen predominantly in older adults, AML includes an accumulation of myeloblasts and a replacement of normal marrow by malignant cells, which leads to impaired hematopoiesis. Clinical presentation consisting of fatigue, bleeding, fever, and infection is related to anemia, thrombocytopenia, and a lack of functional WBCs. The onset of symptoms takes days to weeks. Additional findings in AML may include gingival hypertrophy and skin infiltration (leukemia cutis). Diagnosis is via peripheral blood smear and bone-marrow biopsy examination (shows myeloblasts). The precursor cells contain Auer rods. Immunophenotyping, histochemistry, and genetic analysis all aid in identifying and guiding the treatment of AML. Management is chemotherapy administered in phases (induction, consolidation, and maintenance) based on subtypes. Prognosis varies according to the age of onset and type of leukemia.

The myeloid lineage produces a diverse group of blood cells (leukocytes) involved in the defense of the body against foreign substances or infectious agents. Monocytes, neutrophils, eosinophils, basophils, and mast cells all arise from the common myeloid progenitor (CMP), which develops from bone marrow stem cells. However, leukocytes have different functions. Neutrophils kill invading bacteria and fungi, eosinophils increase in parasitic infections, basophils and mast cells are key to allergic response as sources of histamine, and monocytes are released from bone marrow to become macrophages in the tissues. The development in the bone marrow is regulated by different cytokines.

Lymphocytes are heterogeneous WBCs involved in immune response. Lymphocytes develop from the bone marrow, starting from hematopoietic stem cells (HSCs) and progressing to common lymphoid progenitors (CLPs). B and T lymphocytes and natural killer (NK) cells arise from the lineage. B and T lymphocytes play a role in adaptive immunity, and NK cells provide host defense against atypical proteins such as tumor cells. While all developmental stages begin in bone marrow, lymphocyte maturation differs. B lymphocytes and NK cells differentiate in bone marrow before migrating to secondary lymphoid organs (such as lymph nodes). T lymphocytes, however, proceed to the thymus for further maturation.

Multiple myeloma (MM) is a malignant condition of plasma cells (activated B lymphocytes) primarily seen in the elderly. Monoclonal proliferation of plasma cells results in cytokine-driven osteoclastic activity and excessive secretion of IgG antibodies. Osteoclastic activity results in bone resorption, bone pain, pathologic fractures, and metabolic disturbances. Excessive secretion of antibodies results in proteinuria and associated kidney damage as well as production and tissue deposition of amyloid fibrils. Metabolic disturbances combined with tissue amyloid deposition cause end-organ damage. Diagnosis is established by plasma electrophoresis and bone marrow biopsy. Treatments to slow down the disease progression are available; however, there is no cure for MM. The median survival is approximately 3 years.

Hodgkin lymphoma (HL) is a malignancy of B lymphocytes originating in the lymph nodes. The pathognomonic histologic finding of HL is a Hodgkin/Reed-Sternberg (HRS) cell (giant multinucleated B cells with eosinophilic inclusions). The disease presents most commonly with lymphadenopathy (neck most commonly involved), night sweats, weight loss, fever, and at times, splenomegaly and hepatomegaly. Diagnostic testing includes lymph node histologic analysis showing HRS cells, blood tests, and CT and PET scanning. HL is managed with chemotherapy and radiotherapy. The prognosis has improved significantly with the advent of chemotherapeutic regimens.