Lymph node cytopathology: Essential ancillary studies as applied to lymphoproliferative neoplasms.

Ancillary testing is absolutely integral to the correct recognition and classification of lymphoid neoplasms as procured with the fine-needle aspiration (FNA) biopsy technique. In patients with a newly diagnosed lymphoid neoplasm, immunophenotyping with flow cytometry, immunohistochemistry, or both is a standard that is currently expected by oncologists before any form of therapy is initiated. This is often the case also for patients with recurrent/relapsed disease. The cellular material obtained with FNA is perfectly suited to meet this demand. That said, the exceptional complexity of modern-day lymphoma classification often precludes definitive subclassification in a subset of lymphomas for a variety of reasons with the FNA biopsy technique, even with the application of ancillary tests. These include a requirement for definitive knowledge of the nodal architecture (eg, Hodgkin lymphoma), of the histologic grade via the counting of cells per microscopic field (follicular lymphoma), and of molecular findings (often unobtainable because of limitations of cellularity). The application of molecular tests to lymph node aspirates continues to evolve but is still largely confined to specialized medical centers. The intent of this article is to briefly review the diagnostic approach and algorithm for handling lymph node aspirates at the authors' own laboratory. This article highlights what the authors and others consider to be essential ancillary tests and discusses their respective advantages and shortcomings. It lists limited and extended antibody panels and molecular tests that the authors have found helpful not only for correctly recognizing lymphoma with FNA cytopathology but also for subtyping lymphomas whenever possible.