uses tests to determine whether (1) the RS cells are surrounded by inflammatory cells, and (2) the CD30 antigen and CD15 antigen are present on the RS cells. The hematopathologist may also use more sophisticated molecular tests to help confirm the diagnosis. HL usually starts in the lymph nodes, and the first signs a patient notices may be swelling in the neck, above or below the collarbone, under the arms, in the chest, or in the groin. The lymphoma can then spread throughout the body via lymphatic vessels. HL may also spread to other areas and organs outside of the lymphatic system. What Distinguishes HL From NHL? The RS cells seen in patients with HL are not present in patients with NHL. Also, unlike NHL, HL tends to spread from one group of lymph nodes to adjacent nodes, while NHL may spread to lymph nodes anywhere in the body in an unpredictable manner. The different types and subtypes of HL are distinguished by how they look under a microscope. The two main forms are classical HL (cHL) and nodular lymphocyte-predominant HL (NLPHL). Classical Hodgkin Lymphoma and Its Subtypes About 95 percent of patients with HL have cHL. Classical Hodgkin lymphoma is further divided into four subtypes, as described in Table 1.1. However, it is important to remember that these four subtypes are generally treated similarly. Learning the Basics 16 Part 1 Table 1.1. Subtypes of Classical Hodgkin Lymphoma Nodular Lymphocyte-Predominant Hodgkin Lymphoma NLPHL, which makes up about five percent of HL cases, is characterized by variants of RS cells called lymphocyte-predominant (LP) cells. These are also called “popcorn cells,” because the cell nuclei resemble popped kernels of corn. LP cells have different antigens on their cell surfaces than the RS cells in cHL. For example, LP cells are positive for the CD20 antigen, which is common in B-cell NHL, and they are negative for the CD30 antigen. This form of HL is often found in the lymph nodes of the neck, groin, or underarms. It is indolent (slow-growing). The approach to treatment for NLPHL differs Nodular Sclerosis HL ■ Affects 70 percent of patients with cHL ■ Often causes involved lymph nodes to form nodules (lumps) separated by broad bands of fibrotic (fiber-like) or sclerotic (hardened) tissue ■ Typically affects young adults and is more common in women ■ Most frequently involves lymph nodes in the chest Mixed Cellularity HL ■ Affects 20 to 25 percent of patients with cHL ■ Characterized by many classic RS cells mixed with various other types of inflammatory cells ■ Primarily affects older adults, children under 10 years, and people with underlying immunodeficiency disorders LymphocyteRich HL ■ Affects five percent of patients with cHL ■ Characterized by many normal lymphocytes and relatively few RS cells ■ More common in men LymphocyteDepleted HL ■ Affects less than one percent of patients with cHL ■ Characterized by very few normal lymphocytes and many RS cells ■ More common in older adults ■ Often not diagnosed until the disease is in an advanced stage 17 Understanding Hodgkin Lymphoma from the treatment for cHL, as discussed in Chapter 8. NLPHL should not be confused with lymphocyte-rich HL, which is a subtype of cHL described in Table 1.1. Why Do Certain People Develop HL? The reasons why certain people develop HL are not totally understood. However, scientists have found that people with particular characteristics called “risk factors,” have a slightly higher chance of developing HL compared with people who do not have these risk factors. Having one or more HL risk factors does not mean a person will definitely develop the disease. In fact, most people with the known risk factors never develop HL, and many people diagnosed with HL do not have any of these risk factors. However, there does seem to be a correlation between the risk factors described in Table 1.2 and the development of HL. Table 1.2. Known Risk Factors for Hodgkin Lymphoma Age ■ It has a bimodal distribution of age groups: people who are 15 to 40 years of age, as well as those who are older than 55 years, have a higher risk of developing HL than people in other age groups. Family History ■ People with a family history of HL, especially among