Classification of malignant lymphoma subtypes in Korean patients: a report of the 4th nationwide study

To determine the relative frequency and change of malignant lymphoma in Korea according to the 4th World Health Organization (WHO) classification and compare with previous reports. Between 2015 and 2016, 7737 new patients with malignant lymphoma were enrolled from 31 institutes, with their clinicopathologic information obtained, and evaluated for the relative frequency of lymphoma subtypes. The relative frequency of non-Hodgkin lymphoma (NHL) was 94.8%, and that of Hodgkin lymphoma (HL) was 5.2%. B cell lymphomas accounted for 83.1% of all NHLs; T/natural killer (NK) cell lymphomas, 16.4%; and immunodeficiency-associated lymphoproliferative disorders, 0.5%. The most common NHL subtypes were diffuse large B cell (41.5%), extranodal marginal zone (MALT, 19.8%), follicular (7.5%), NK/ T cell (4.2%), and peripheral T cell lymphomas, not otherwise specific (PTCL, NOS, 3.4%). Nodular sclerosis was the predominant HL subtype (48.5%), followed by mixed cellularity (28.7%), lymphocyte-rich (6.8%), lymphocyte-depleted (1.5%), lymphocyte-predominant (2.8%), and unclassified HL (11.8%). Compared with a previous report, increased B cell lymphomas (77.6–83.1%) and slightly decreased NK/T cell lymphomas and PTCL were observed. The incidence of follicular lymphoma increased by more than 2.5-fold (2.9–7.5%). Incidence rates of newly diagnosed lymphomas were lower for HL and higher for extranodal NHL, MALT, and nasal type NK/T cell lymphomas in Korea than those in Western countries. A slight increase in the relative frequency of B cell lymphoma and a prominent increase in follicular lymphoma may be attributed to refined diagnostic criteria and Westernized disease patterns.