Follicular lymphoma (FL) is the most common type of indolent (low-grade) B-cell lymphoma that accounts for 10 to 20% of all non-Hodgkin lymphomas. The prevalence of FL has recently been increasing in Japan. FL is histopathologically classifed into grades 1, 2, 3A, and 3B, but grade 3B is typically treated as aggressive (intermediate- to high-grade) lymphoma. It is diagnosed from lymph node enlargement in almost all patients, and about 70 to 85% of patients have advanced (clinical stage III/IV) disease on diagnosis, and bone marrow involvement is frequently observed as well. Although there has recently been much attention on extranodal FL localized to the gastrointestinal tract or skin, these guidelines will primarily cover nodal FL. FL typically has an indolent course and initially responds well to chemotherapy. However, it is typical for FL patients to experience repeated relapses, and this trend is particularly strong with advanced disease. An analysis conducted after the introduction of rituximab showed that histologic transformation to aggressive lymphoma occurred in about 10% of patients over a 5- to 10-year period. Although median survival time for FL patients was previously considered to be 7–10 years based on data from before the introduction of rituximab, recent studies have shown median survival time of over 20 years for patients diagnosed at age 40 or younger.

滤泡性淋巴瘤（FL）是最常见的惰性（低级别）B细胞淋巴瘤，约占所有非霍奇金淋巴瘤的10%~20%。近年来，日本FL的患病率呈上升趋势。

FL在组织病理学上分为1级、2级、3A级和3B级，其中3B级通常按侵袭性（中至高级别）淋巴瘤治疗。几乎所有患者均因淋巴结肿大就诊，约70%~85%的患者确诊时已为晚期（临床III/IV期）病变，且常伴有骨髓受累。尽管近年来局限于胃肠道或皮肤的结外FL备受关注，但本指南将主要聚焦于结内FL。

FL通常病程惰性，初期对化疗反应良好。然而，FL患者往往会出现反复复发，这种趋势在晚期患者中尤为明显。利妥昔单抗应用后的相关分析显示，约10%的患者在5~10年内会发生组织学转化，进展为侵袭性淋巴瘤。基于利妥昔单抗应用前的数据，FL患者的中位生存期曾被认为是7~10年；但近期研究表明，40岁及以下确诊患者的中位生存期已超过20年。