Transformed follicular lymphoma
FL progresses at a rate of 2-3% per year for at least the first 10 years after diagnosis to a more aggressive form, principally diffuse large B-cell lymphoma (~93% of cases) or Burkitt-like lymphoma (~7% of cases) or in rare cases exhibit the histology resembling precursor B-cell lymphoblastic leukemia, plasmablastic lymphoma, the high grade subtype of B-cell lymphoma, Hodgkin lymphoma of the B-cell type, chronic lymphocytic leukemia/small cell lymphcytic lymphoma, or histiocytic sarcoma. t-FL is almost always diagnosed in patients being followed for FL. These FL patients present with the: fast growth of lymph nodes; formation of extra-nodal lesions in extra-nodal sites such as the central nervous system, liver or bone; the onset of B-symptoms (i.e. fever, night sweats, weight loss); development of hypercalcemia (i.e. high serum levels of calcium); and/or sudden rises in serum levels of the enzyme lactate dehydrogenase. A minority of t-FL patients present without a history of FL. These patients generally present with advanced, bulky disease that may be accompanied by extra-nodal lesions and B-symptoms. Typically, all the various forms of t-FL are aggressive, rapidly progressive diseases with overall media survival times in treated patients of ~4.5 years. The transformation of FL to DLBCL is in over 70% of cases associated with the gain of MYC activity by genetic or non-genetic mechanisms. Diagnosis
The diagnosis of FL depends on examining involved tissues for histological, immunological, and chromosomal abnormalities that are indicative of the disease.
Grade 2: follicles have 6 to 15 centroblasts per hpf. Grade 3: follicles have >15 centroblasts per hpf. Grade 3A: Grade 3 in which the follicles contain predominantly centrocytes. Grade 3B: Grade 3 in which the follicles consist almost entirely of centroblasts.Grades 1 and 2 are regarded as low grade FL; Grade 3A is usually also regarded as low grade FL although some studies have regarded it as high grade FL; and Grade 3B is regarded as a highly aggressive FL in the t-FL category.In addition to grade 3B disease, histologic examinations may reveal other evidence of t-FL such as histologic findings consistent with FL and diffuse large cell lymphoma in the same tissue (referred to as composite lymphomas) or in separate tissues (referred to as (discordant lymphomas) or histologic findings similar to those found in Burkitt lymphoma, precursor B-cell lymphoblastic leukemia, plasmablastic lymphoma, the high grade subtype of B-cell lymphoma, Hodgkin lymphoma of the B-cell type, chronic lymphocytic leukemia/small cell lymphocytic lymphoma, or histiocytic sarcoma. Other findings indicating the presence of this transformation include rapid growth in size of lymph nodes, recently acquired or new B symptoms, recent development of FL lesions in non-nodal tissue, rapid rises in serum lactate dehydrogenase levels, and the presence of high levels of serum calcium. Differential diagnosis
FL may be confused with marginal zone B-cell lymphoma, mantle cell lymphoma, and the small lymphocytic lymphoma variant of chronic lymphocytic leukemia.