“Double hit” follicular lymphoma with low proliferation index: A unique case and literature review

“Double hit” lymphomas (DHLs) are aggressive B-cell lymphomas with concurrent c-MYC and BCL2 and/or BCL6 gene rearrangements. DHLs are usually classified morphologically as B-cell lymphoma, unclassifiable, with features intermediate between diffuse large B-cell lymphoma (DLBCL) and Burkitt lymphoma, and less commonly as DLBCL. Follicular lymphoma (FL) is characterized genetically by the presence of IGH-BCL2 rearrangement. A subset of DHLs arises from FL by the acquisition of c-MYC gene rearrangement during disease progression, but FL with concurrent IGH-BCL2 and c-MYC gene initial rearrangements is rarely reported. The few reported cases had different clinical courses, including some with indolent disease. We report a case of “double hit” low grade FL with both c-MYC and BCL2 gene rearrangements but at low proliferation rate. Unlike the usual DHLs with aggressive clinical course, our patient showed at least partial response to intense chemotherapy. Review of the literature shows a few similar cases with variable clinical course, including a few indolent cases. These patients appear to respond better with more intense chemotherapy for DHL.