Low-grade lymphomas can be difficult to diagnose in cytology specimens, especially marginal zone B-cell lymphomas (MZLs). MZL is a low-grade lymphoma characterized by a heterogeneous lymphoid population, which can be difficult to distinguish from reactive processes in cytology specimens.
Fourteen cytology specimens of MZL from 11 patients with histologically confirmed MZL (n = 10) or flow cytometry (FC)-confirmed MZL (n = 1) were reviewed, including 13 fine-needle aspiration biopsy (FNAB) specimens (salivary gland, n = 6; lung, n = 3; lymph node, n = 2; breast, n = 1; and soft tissue, n = 1) and 1 pleural effusion specimen. Cytologic preparations included air-dried and alcohol-fixed direct smears, ThinPrep(R) slides, and cell blocks. FC studies were available in six specimens.
All 13 FNAB specimens were composed predominantly of intermediate-sized lymphoid cells with interspersed small, round lymphocytes and transformed cells. The intermediate-sized cells displayed a moderate amount of cytoplasm, slight nuclear membrane irregularities, and inconspicuous-to-absent nucleoli. The pleural fluid contained mostly small-to-intermediate-sized, round lymphocytes. In 10 specimens, the intermediate-sized cells often showed plasmacytoid morphology, which were seen best in Diff-Quik (Mercedes Scientific Co., Inc., Sarasota, FL)-stained slides. Monocytoid cells (n = 6 specimens), plasma cells (n = 7), lymphohistiocytic aggregates (n = 11), and tingible body macrophages (n = 5) were variably identified. Lymphoepithelial lesions were not observed. Three specimens with FC studies showed a phenotype compatible with MZL, and three specimens were nondiagnostic.
Cytologic features suggestive of MZL included abundant intermediate-sized lymphoid cells with mild atypia in a background of small lymphocytes and transformed cells, often with plasmacytoid morphology. Flow cytometry was beneficial only in selected MZL cytology specimens. Surgical correlation may be necessary to confirm the diagnosis.