Follicular lymphoma is also referred to as follicle centre cell lymphoma and was previously known as poorly differentiated lymphocytic lymphoma and centroblastic/centro cytic lymphoma. It is a disease of adult life, occurring in young, middle aged and elderly adults. It is rare in children and adolescents. In contrast to most other lymphoproliferative disorders, there is a somewhat higher incidence in women. It is a low-grade malignancy. Although many patients (around 80%) present with widespread disease, median survival is of the order of 9 to 10 years. Follicular lymphoma arises from a germinal centre B cell showing ongoing somatic hypermutation of IGVH.
Patients usually present with lymphadenopathy . Sometimes the spleen is also enlarged and Waldeyer's ring may be involved. Occasionally the diagnosis is incidental in an asymptomatic patient. Even widespread disease is often relatively asymptomatic but some patients with advanced disease have B symptoms (fever, weight loss and night sweats). Patients with advanced disease may have pleural or pericardial effusions or ascites. Spontaneous remissions, with subsequent relapse, are sometimes observed. Rarely, a spontaneous remission occurs and on prolonged follow-up there is no relapse. Transformation to diffuse high-grade B-cell lymphoma can occur. Follicular lymphoma of the skin differs somewhat from other follicular lymphomas in its pathological features.
Haematological and pathological features
The peripheral blood may be normal or there may be a greater or lesser number of circulating lymphoma cells . Cytological characteristics differ between patients (Figures 5.1, 5.2, 5.3). Some patients, particularly those with large numbers of circulating lymphoma cells, have very small cells, smaller than those of chronic lymphocytic leukaemia, with scanty cytoplasm; the nuclei show evenly condensed (rather than clumped) chromatin and deep, very narrow clefts. In other patients the cells are larger and more pleomorphic with less condensed cytoplasm and often a visible nucleolus; some cells have nuclear clefts, which are characteristically deep and narrow with parallel edges. Cells are less fragile than those of chronic lymphocytic leukaemia so that smear cells are less often a feature. Anaemia and thrombocytopenia are uncommon at presentation, but may be seen in patients with advanced disease.
Peripheral blood film in follicular lymphoma showing mature lymphocytes with cleft nuclei and condensed chromatin. Romanowsky, x 60 objective.
Peripheral blood film in follicular lymphoma showing showing mature lymphocytes with very scanty cytoplasm and in two of the three cells, cleft or notched nuclei; chromatin is fairly evenly condensed. Romanowsky, x 100 objective.
Peripheral blood film in follicular lymphoma showing two lymphoma cells, one of which has a nuclear cleft. Romanowsky, x 100 objective.