Marginal zone B-cell lymphoma

Marginal zone B-cell lymphomas, also known as marginal zone lymphomas (MZLs), are a heterogeneous group of lymphomas that derive from the malignant transformation of marginal zone B-cells. Marginal zone B cells are innate lymphoid cells that normally function by rapidly mounting IgM antibody immune responses to antigens such as those presented by infectious agents and damaged tissues. They are lymphocytes of the B-cell line that originate and mature in secondary lymphoid follicles and then move to the marginal zones of mucosa-associated lymphoid tissue (i.e. MALT), the spleen, or lymph nodes. Mucosa-associated lymphoid tissue is a diffuse system of small concentrations of lymphoid tissue found in various submucosal membrane sites of the body such as the gastrointestinal tract, mouth, nasal cavity, pharynx, thyroid gland, breast, lung, salivary glands, eye, skin and the human spleen. In 2016, the World Health Organization classified MZLs into three different types. Extranodal marginal zone lymphomas (EMZLs) are MZLs that develop in extranodal tissues. Most EMZLs develop in MALT and are often termed extranodal MZL of mucosa-associated lymphoid tissue or, more simply, MALT lymphomas. Splenic marginal zone lymphomas (SMZLs) are MZLs that initially are confined to the spleen, bone marrow, and blood. Nodal marginal zone lymphomas (NMZs) are MZLs initially confined to lymph nodes, bone marrow, and blood. While all of these MZL involve malignant B-cells, they differ not only in the tissues they involve but also in their pathophysiology, clinical presentations, prognoses, and treatments. MZLs represent 5–17% of all Non-Hodgkin lymphomas with the extranodal, splenic, and nodal forms accounting for 50–70%, ~20%, and ~10% of all MZLs. The three MZL subtypes occur more often in older people (age 65–68 years) and are indolent diseases that may, in people without symptoms, be initially treated by a watchful waiting strategy.