Sadahiro Asai

A T‐cell neoplasia showing clinicopathologic features of malignant histiocytosis with novel chromosomal abnormalities and N‐ras mutation

Malignant histiocytosis (MH) is a distinct disease entity defined clinically and morphologically. However, the neoplastic origin of MH is not well established. The authors report a 26‐year‐old woman who showed the typical clinicopathologic features of so‐called MH. Cytogenetic and molecular genetic examinations were performed in addition to the morphologic and immunologic approach. The expression of CD2 and T‐cell receptor gene rearrangements indicated the T‐cell origin of this case. CD30, which is positive for anaplastic large cell lymphoma (Ki‐1 lymphoma), was not expressed. The cytogenetic study revealed a clonal chromosome abnormality involving 3q25, 6p21, 11p15, and 11q21. An N‐ras point mutation within codon 12 (GGT→GCT) was also detected. These findings indicate that MH defined clinically and morphologically is not a tumor of true histiocytic origin and that it should be reclassified on the basis of immunologic, cytogenetic, and molecular genetic data.