Regressing atypical histiocytosis: report of two cases with progression to high grade T-cell non-Hodgkin's lymphoma.

Two cases of regressing atypical histiocytosis (RAH) are presented. Both patients followed a typical regressing/relapsing course for several years before progression to high-grade neoplasia. In both cases these high-grade tumors were diagnosed as T-cell non-Hodgkin's lymphoma on histopathologic and immunophenotypic grounds, and demonstrated T-cell receptor beta chain (TCR beta) gene rearrangement on Southern blotting. The original cases of RAH were considered to be indolent neoplasms of histiocytic lineage. A single case of a patient with RAH demonstrating TCR beta and gamma gene rearrangements has been described. Our cases lend further weight to the proposition that RAH is a neoplasm of T-cell lineage, and ultimately of aggressive potential. This description accords with current thinking that many of the conditions previously classified as malignant histiocytosis would be better classified as T-cell non-Hodgkin's lymphoma.