Lymphoma is a type of cancer that affects the lymphatic system, particularly the white blood cells called lymphocytes which work as protection against infections and diseases. Lymphocytes affected by the disease reproduce faster instead of normally dying and giving space to new cells. Lymphoma develops in different parts of the body, in particular, the lymph nodes, and its first manifestation is swollen, painless lymph nodes. There are different types of lymphomas, with the most common denomination being Hodgkin lymphomas and non-Hodgkin lymphomas.
The Hodgkin lymphomas are the rarest types of the disease and are characterized by Reed-Sternberg cells. There are six different subtypes of Hodgkin lymphoma. This type of cancer has several unique characteristics, which can be discovered when observed under a microscope. According to World Health Organization (WHO) classification, there are four types of classical Hodgkin lymphoma, which are called nodular sclerosing, mixed cellularity, lymphocyte rich, and lymphocyte depleted, as well as two types of nodular lymphocyte predominant Hodgkin lymphoma, which are rare and occur only in one out of 20 cases of the disease.
Non-Hodgkin lymphomas are the most common and there are around 61 known types of the disease. Unlike Hodgkin lymphoma, Non-Hodgkin lymphoma does not involve Reed-Sternberg cells. It is difficult to compile all types of Non-Hodgkin lymphoma due to the great amount and different methods used to do so. Therefore, the current standard classification is the one defined by the WHO, which is based on its appearance when analyzed under a microscope, the chromosome features of the lymphoma cells, the existence of certain proteins, and whether it is originated in B-cells or T-cells.