Evaluation of lymphoid cell populations in cytology specimens using flow cytometry and polymerase chain reaction

Differential diagnosis between lymphomas and reactive lymphoid proliferatio ns often requires ancillary techniques and morphologic evaluation. Flow cyt ometry (FCM) and polymerase chain reaction (PCR) can aid the detection of m onoclonal B-cell populations. In the present study, the sensitivity and spe cificity of these two methods in the study of cytology specimens were compa red. Eighty-six cytologic specimens from 81 patients (lymph nodes, solid or gans, and body cavities) were evaluated. These specimens were taken from th ree groups of patients: those who underwent an initial evaluation for suspe cted lymphoma; those who were previously diagnosed with B-cell lymphoma and were now evaluated for possible disease recurrence; and those who were dia gnosed with a nonhematologic malignancy. Histologic diagnosis was available for 51 samples. All samples were tested by FCM for the detection of monocl onality using kappa:lambda ratio and for clonal immunoglobulin heavy chain (IgH) gene rearrangements using a single-round PCR after cytologic evaluati on. Tissue morphology, FCM and PCR results, and clinical findings in specim ens without histologic diagnosis were correlated. Histologic evaluation (N = 51) revealed 44 specimens with B-cell malignancy. Twenty of the 44 lympho ma specimens (45%) were accurately diagnosed in cytologic smears, 18 (41%) were classified as suspicious of lymphoma, and 6 (14%) were diagnosed as re active. FCM had superior sensitivity compared with PCR (77% vs. 64%). Fifty -six percent of specimens with B-cell malignancy were FCM+/PCR+, 23% were F CM+/PCR-, 14% were FCM-/PCR+, and 7% were FCM-/PCR-. The combined use of FC M and PCR resulted in a diagnosis of B-cell lymphoma in 41 (93%) of 44 B-ce ll lymphoma specimens and increased the sensitivity of fine needle aspirati on by 48%. Both FCM and PCR aid in the diagnosis of lymphoid lesions in cyt ology specimens, and both can detect monoclonal B-cell populations that may be interpreted in cytology smears as reactive, even by experienced cytolog ists. Although FCM had higher sensitivity than PCR test in the present stud y, their combined use should be considered because of a relatively large nu mber of specimens that were detected as monoclonal only with PCR.