Composite Follicular Lymphoma and CD5-Positive Nodal Marginal Zone Lymphoma

The broad landscape of follicular lymphoma: Part II

Follicular lymphoma is a neoplasm derived from follicle center B cells, typically both centrocytes and centroblasts, in variable proportions according to the lymphoma grading. The pattern of growth may be entirely follicular, follicular and diffuse and rarely completely diffuse. It represents the second most common non-Hodgkin lymphoma, after diffuse large B-cell lymphoma and it is the most common low-grade mature B-cell lymphoma in Western countries. In the majority of cases, follicular lymphoma is a nodal tumor, occurring in adults and is frequently associated with the translocation t(14;18)(q32;q21)/IGH-BCL2. However, in recent years the spectrum of follicular lymphoma has expanded and small subsets of follicular lymphoma, which differ from common follicular lymphoma, have been identified and included in the current 2017 WHO classification. The aim of our review is to describe the broad spectrum of follicular lymphoma, pointing out that the identification of distinct clinicopathological variants of follicular lymphoma is relevant for the patient outcomes and treatment.

Two for One: B-Cell Lymphomas with Features of Marginal and Follicular Lymphomas

Low-grade follicular lymphomas are genetically characterized by the translocation t(14; 18)(q32;q21) with BCL2 gene rearrangements. Marginal zone lymphomas are often associated with translocations or transcriptional deregulations of the MALT gene. We report 2 cases of lymphomas which harbor both the t(14;18)(q32;q21) translocation and MALT gene upregulation. Patients presented with numerous circulating atypical lymphocytes. Lymph node biopsy in both cases on HE staining demonstrated vague nodularity readily highlighted by CD10, CD23, or BCL6. Staining with CD20 and BCL2 demonstrated monotonous diffuse effacement of normal architecture with tumor cells without obvious follicular structures. Morphologically, tumor cells were consistent with centrocytes. Bone marrow biopsy demonstrated a combined peritrabecular and interstitial distribution of the tumor cells. These cases present substantial difficulties for diagnosis and classification. Clinical and morphological features were mostly consistent with follicular lymphoma, with a few features more often seen in marginal zone lymphomas (leukemic presentation, no CD10 in circulating cells, interstitial location of tumor cells in bone marrow); therefore, these cases were finally classified as follicular lymphoma grade I. Both patients were treated with standard chemotherapy regimens for follicular and nongastric MALT lymphomas with a good response to date.