Immunoperoxidase stain for the S100 protein.
Immunoperoxidase stain for the cytokeratin antigens AE1/3.
Immunoperoxidase stain for the leukocyte common antigen.
Immunoperoxidase stain for B lymphocytes (CD 20).
Immunoperoxidase stain for T lymphocytes (CD43, L60).
Immunoperoxidase stain for IgM.
Microscopic examination reveals a nodular mass comprised of cells with finely stippled ("salt and pepper") nuclei, prominent, usually single nucleoli, and scant cytoplasm. There are numerous mitotic figures, occasional individual necrotic cells, and sparse eosinophils. The edge of the tumor is infiltrative. A desmoplastic reaction is not seen.
The tumor cells are strongly positive for leukocyte common antigen and CD20 and negative for CD43, S-100, HMB45, and AE1/AE3.
Results of immunoperoxidase stains for immunoglobulins in formalin fixed tissue are as follows: IgM positive, IgA negative, IgG negative, IgD negative, Kappa negative, Lambda negative.