FISH detection of t(14;18) in follicular lymphoma on Papanicolaou-stained archival cytology slides

BACKGROUND: The t(14;18)(q32;q21) translocation is present in about 85% of follicular lymphomas (FL) and can be identified using fluorescence in situ hybridization (FISH). In the diagnostic laboratory setting, the cytologic archival material consists of stained slides, and only rarely is material saved for molecular testing. The authors proposed FISH for FL using Papanicolaou-stained archival cytology material as a practical ancillary technique for diagnosing FL. METHODS: Cases included 35 FL, 6 small lymphocytic lymphomas/chronic lymphocytic leukemias (SLL/CLL), 4 mantle cell lymphomas (MCL), 4 marginal zone lymphomas (MZL), 1 lymphoplasmacytic lymphoma (LPL), and 10 reactive lymphoid tissues (RLT). FISH was performed on Papanicolaou-stained archival cytology slides using probes for immunoglobulin heavy chain (IGH) on chromosome 14 and BCL2 on chromosome 18. RESULTS: In all, 25 of 32 (81%) FL cases exhibited the t(14;18) translocation, whereas 7 of 32 (19%) lacked the translocation. No cases of non-FL were positive for t(14;18). This series shows a sensitivity of 81% and specificity of 100% for detecting the t(14;18) translocation as a diagnostic tool in FL. CONCLUSIONS: When performed on Papanicolaou-stained cytology slides, FISH for t(14;18) is relatively sensitive and quite specific for FL. These findings are similar to those reported on other specimens, such as paraffin-embedded tissue and unstained cytology slides. The authors proposed that their technique would allow the pathologist and clinician the flexibility to utilize previously stained fine-needle aspiration slides for FISH evaluation.