Malignant B cell characteristics High-power view of<unk>  with "starry sky" appearance. H&E stain.Normal B cells of a germinal center possess rearranged immunoglobulin heavy and light chain genes, and each isolated B cell possesses a unique IgH gene rearrangement. Since<unk>  and other B-cell lymphomas are a clonal proliferative process, all tumor cells from one patient are supposed to possess identical IgH genes. When the DNA of tumor cells is analyzed using electrophoresis, a clonal band can be demonstrated, since identical IgH genes will move to the same position. On the contrary, when a normal or reactive lymph node is analyzed using the same technique, a smear rather than a distinct band will be seen. This technique is useful since sometimes benign reactive processes (e.g. infectious mononucleosis) and malignant lymphoma can be difficult to distinguish. Microscopy<unk>  in a kidney biopsy. The tumor consists of sheets of a monotonous (i.e., similar in size and morphology) population of medium-sized lymphoid cells with high proliferative and apoptotic activity. The "starry sky" appearance seen under low power is due to scattered tingible body-laden macrophages (macrophages containing dead apoptotic tumor cells). The old descriptive term of "small non-cleaved cell" is misleading. The tumor cells are mostly medium in size (i.e., tumor nuclei size similar to that of histiocytes or endothelial cells). "Small non-cleaved cells" are compared to "large non-cleaved cells" of normal germinal center lymphocytes. Tumor cells possess small amounts of basophilic cytoplasm with three to four small nucleoli. The cellular outline usually appears squared off. Immunohistochemistry The tumor cells in<unk>  generally strongly express markers of B cell differentiation (CD20, CD22, CD19), as well as CD10 and BCL6. The tumor cells are generally negative for BCL2 and TdT. The high mitotic activity of<unk>  is confirmed by nearly 100% of the cells staining positive for Ki67.
Burkitt lymphoma
Hodgkin lymphoma
AIDS-related lymphoma
Thymic carcinoma
B-cell lymphoma
Thymoma with immunodeficiency
Diffuse large B-cell lymphoma
Mantle cell lymphoma