OBJECTIVETo assess the value of histologic examination, immunohistochemistry and gene rearrangement studies in the diagnosis and subtyping of lymphoma with bone marrow involvement (BMI).

METHODSSixty-two formalin fixed, paraffin embedded bone marrow biopsy specimens were studied. Immunohistochemical and immunoglobulin heavy chain (IgH) and T-cell receptor gene rearrangement studies were performed in each case.

RESULTSChronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) demonstrated mainly and interstitial infiltration by dysplastic lymphocytes, with intertrabecular nodular arrangement or in dispersion. Sometimes, pseudofollicles may be noted. A predominantly para- or intertrabecular infiltration by nodules of lymphoma cells was characteristic of follicle center cell lymphoma (FCL) cases. In most lymphoplasmacytoid lymphoma (LPL) cases, there was infiltration by small lymphocytes and plasma cells between bony trabeculae. In marginal zone cell lymphoma (MZL), vague inter- or para-trabecular nodules of polymorphic lymphoma cells with clear cytoplasm might be noted. Small to medium-sized dysplastic lymphocytes, with absence of paraimmunoblasts or pseudofollicles, were the most frequent findings in mantle cell lymphoma (MCL). Hairy cell leukemia (HCL) might be identified by the presence of distinct cell membrane and abundant clear cytoplasm, resulting in a "fried-egg" appearance. Tumor cells with large nuclei and eosinophilic nucleoli were characteristically seen in lymphomatosis diffusa (Hodgkin's disease, HD). In T-cell non-Hodgkin lymphoma with BMI, dispersed or clusters of intertrabecular neoplastic lymphoid cells with clear cytoplasm and gyriform nuclei were often observed. In diffuse large B-cell lymphoma (DLBL), the tumor cells were large and isolated or arranged in diffuse pattern. Immunohistochemically, a panel of markers, including CD3 CD20, and CD79 are valuable for the differential diagnosis of T- and B-cell lymphomas. The neoplastic cells in MCL were cyclin D1- and CD5-positive, while BCL2- and CD10-positivity was characteristic for FCL. CLL/SLL cells might be stained with CD5 and CD23, in addition to CD20 and CD79. CD25 expression might be noted in HCL: the positivity for CD15, CD30 and fascin suggests HD. There was a higher positivity rate for IgH gene rearrangement in CLL/SLL, LPL MZL and DLBL (80%, 60%, 66.7%, 70% respectively) and for T- cell receptor gamma gene rearrangement in T-cell lymphoma (66.7%).

CONCLUSIONA combination of histopathology, immunohistochemistry and IgH / T-cell receptor gamma gene rearrangement studies may be of aid to the diagnosis and subtyping of lymphoma with BMI, especially if there is only a small number of tumor cells present in the specimen.