In situ follicular lymphoma associated with overt B- or T-cell lymphomas in the same lymph node

In situ follicular lymphoma (FL) is usually an incidental finding in otherwise reactive lymph node [1-3]. However, it may be associated with overt FL, or with lymphomas other than FL or with other malignancies, in other sites or, less commonly, in the same lymph node [2,4-8]. Here we describe two cases of in situ FL, one with concurrent overt FL (Case 1), and one with concurrent peripheral T-cell lymphoma (PTCL), NOS (Case 2) in the same lymph node. Immunohistochemistry, polymerase chain reaction for B and T-cell clonality, and double-staining chromogenic in situ hybridization for BCL2 translocation were performed. In both cases, the in situ FL foci were characterized by strong expression of BCL2 and CD10 in the germinal center B cells of the affected follicles. Case 1 showed the concurrence of an overt B-cell FL with IgH@ rearrangement and expression of B-cell markers, but not BCL2. Case 2 demonstrated the concurrence of a PTCL, NOS with TCRG@ rearrangement and expression of T-cell markers. In conclusion, the association of in situ FL with PTCL expands the spectrum of lymphoproliferations that may coexist with in situ FL and suggests that in situ FL may not behave like a simple precursor for overt FL.