Clinical meaning
Lymphomas are a diverse group of malignant neoplasms arising from lymphocytes within the lymphatic system. The lymphatic system is a network of lymph nodes, lymphatic vessels, the spleen, thymus, tonsils, and bone marrow that functions as a critical component of the immune system. Lymphomas are broadly classified into two major categories: Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL), which differ in their cellular origin, pathological features, clinical behavior, and treatment approach. Hodgkin lymphoma is characterized by the presence of the Reed-Sternberg cell, a large binucleated or multinucleated cell with prominent eosinophilic nucleoli that give it a distinctive owl-eye appearance on microscopy. Reed-Sternberg cells are derived from germinal center B lymphocytes that have undergone malignant transformation. These cells typically comprise only 1-2% of the tumor mass; the remainder consists of a reactive inflammatory infiltrate of normal T cells, B cells, macrophages, eosinophils, and fibrotic tissue. Hodgkin lymphoma has a bimodal age distribution with peaks in young adults (15-35 years) and older adults (over 55 years), and it typically spreads in a predictable, contiguous pattern from one lymph node group to adjacent groups along lymphatic pathways. Non-Hodgkin lymphoma encompasses more than 60 subtypes arising from either B lymphocytes (85%) or T lymphocytes (15%) at various stages of differentiation. Unlike Hodgkin lymphoma, NHL tends to spread in a non-contiguous pattern and is more likely to involve extranodal sites (GI tract, skin, bone, brain) at presentation. NHL is further classified as indolent (low-grade, slow-growing such as follicular lymphoma) or aggressive (high-grade, rapidly growing such as diffuse large B-cell lymphoma [DLBCL]). Paradoxically, aggressive lymphomas are often more curable than indolent lymphomas because rapidly dividing cells are more susceptible to chemotherapy and radiation, while indolent lymphomas may be managed initially with watchful waiting but tend to recur repeatedly over years.