[Diagnosis of orbital lymphoma by molecular genetic analysis]

Recent advances in molecular genetics have made a great contribution to the investigation of lymphoid malignancies. We diagnosed orbital malignant lymphomas by molecular genetic analysis. Molecular genetic analysis elucidates gene rearrangements within lymphocytes that are responsible for immunoglobulin produced by B-lymphocytes, or the expression of cell surface antigen recognition receptors in T-lymphocytes. The cells of most malignant tumors are considered to be genetically homogeneous because they are assumed to represent a single clone descended from one abnormal cell. The determination that a malignancy is of clonal origin has been used as a diagnostic aid to distinguish benign from malignant proliferations. Analysis of the immunoglobulin genes and the T-cell antigen receptor genes using DNA from biopsied specimens is very useful, as it can reveal the origin of tumor cells and clonality of tumor cell characteristics which cannot be distinguished by morphological analysis. Genetic analysis was found to be superior to immunophenotyping for identifying the monoclonality of tumor cells in instances when there were no definitive cell-lineage specific markers, or when there was a preponderance of normal counterparts with mixed appearance of neoplastic and non-neoplastic cells in malignant lymphoma. Molecular genetic analysis is used to 1) distinguish clonal from polyclonal lymphoproliferations, 2) determine the B-cell or T-cell identity of malignancies with admixed normal cells, 3) determine the genetic lineage of neoplasms lacking definitive surface antigens, and 4) determine the developmental stage of early B-cell or T-cell precursors.