Assessment of bone marrow involvement in non-Hodgkin's lymphomas: comparison between histology and flow cytometry

Bone marrow (BM) examination is essential in the staging of non-Hodgkin's lymphoma (NHL) patients. Few studies have compared BM histologic findings with results of flow cytometric (FC) analysis. We analyzed the incidence and patterns of histologic BM involvement in a series of 753 patients with NHL. For 498 patients, a concurrent FC analysis on BM was available. Histologic involvement was detected at diagnosis in 311/753 (41%) patients. By FC, BM involvement was clearly detected in 150/498 (30%). After excluding 12 cases with equivocal histology, concordance between the two methods was detected in 411 (85%) cases (27% BMB+/FC+; 58% BMB-/FC-), while discordance was present in 75 (15%) (P < 0.001): 58 cases (12%) were BMB+/FC- and 17 (3%) were BMB-/FC+. Discordance was more frequent in FL and in lymphoplasmacytic lymphoma (LPL). These data demonstrate that the two methods are comparable in qualitative assessment of BM involvement in NHL, with the exception of FL and LPL. In FL, diffuse large B-cell lymphoma (DLBCL) and LPL, FC underestimates the extent of infiltrate with respect to histology.