Lymphomas are solid cohesive masses of the immune system, originated from the lymphoid tissue. They come from immature precursor of lymph cells called lymphoblasts, but sometimes may also come from more mature lymphocytes. Lymphocytes are white blood cells, roughly divided into T lymphocytes, B lymphocytes and plasma cells (mature B cells). These white blood cells are formed and matured from lymphoblast cells. This maturation process occurs in the bone marrow, the thymus and the lymph nodes.
Most lymphomas are B cell lymphomas. The World Health Organization has classified lymphomas as non-Hodgkin lymphoma, Hodgkin lymphoma, Lymphocytic leukemias, and plasma cell dyscrasias.
Hodgkin lymphomas are classified as classical and variant. The classical type includes nodular sclerosing HL, mixed cellularity HL, lymphocyte rich HL, and lymphocyte depleted HL. The variant type is a nodular lymphocyte-predominant HL.
The classification of Non-Hodgkin lymphomas is wider because it includes everything that is not considered a Hodgkin lymphoma. That includes Precursor B cell lymphoma/leukemia, precursor T cell lymphoma/leukemia, small lymphocyte lymphoma/chronic lymphocytic leukemia, follicular lymphoma, mantle cell lymphoma, diffuse large B cell lymphoma (DLBL), and Burkitt lymphoma.
The causes of lymphomas are diverse. Some of them are spontaneous mutations in the B cells due to chromosome translocations. Other lymphomas are associated with virus infections, especially Epstein-barr virus (EBV) which trigger DLBL in patients with AIDS and other immune deficiencies. Human herpes virus 8 can also cause DLBL in AIDS patients. The causes of Hodgkin lymphoma are unknown, but they are 3 times more likely in patients with infectious mononucleosis caused by EBV.
The clinical features of lymphomas are,
Age and sex
Precursor T cell lymphomas and precursor B cell lymphomas predominantly occur in childhood. All other types are more common in adult life. Small cell lymphoma/chronic lymphocytic leukemia is seen in the elderly, similar to follicular lymphoma, the second most common lymphoma in adults.