[Extranodal lymphomas: current diagnostic approaches in the solution of a Babylonian concept confusion]

A short overview of the development of peripheral B and T lymphocytes is given. Reliable diagnosis of peripheral extranodal lymphomas frequently residing in the mucosa associated lymphoid tissue (MALT) became possible as soon as immunohistochemical staining of monotypic immunoglobulin was available. The importance of the detection of lymphocytic clones for diagnostic purposes is illustrated by selected examples of former misnomers. Light chain restriction of a given lymphocytic infiltrate--together with morphological criteria--is a strong argument in favour of a neoplastic and against a reactive disorder. Immunohistochemically detected monoclonality of MALT lymphomas has recently been confirmed by techniques applied in molecular biology. The temporal and possibly causal relationship of autoimmune disease and certain MALT lymphomas is discussed.