Fluorescence in situ hybridization study of chromosome 7 aberrations in hepatosplenic T-cell lymphoma: Isochromosome 7q as a common abnormality accumulating in forms with features of cytologic progression

Hepatosplenic gammadelta T-cell lymphoma (HSgammadeltaTCL) is a rare and aggressive subtype of peripheral T-cell lymphoma that has been associated cytogenetically with the isochromosome 7q [i(7)(q10)]. The incidence of this aberration and its relevance to pathogenesis of HSgammadeltaTCL is still unknown. We investigated the status of chromosome 7 in 12 HSTCL cases, including nine with a typical gammadelta phenotype, one with a so-called T-cell receptor (TCR)-silent phenotype, and two with the variant alphabeta phenotype. We analyzed available fresh and archival material using a dual-color interphase fluorescence in situ hybridization (FISH) approach with 7p and 7q probes. A significant population of cells with predominance of 7q signals was detected in 10 cases (eight gammadelta, one alphabeta, and one TCR silent), and two lymphomas did not show clonal 7p/7q signal imbalances. In four of 10 cases with chromosome 7 aberrations, a hybridization pattern indicative of the presence of one chromosome 7 and one i(7)(q10) was found. In four other cases, the configuration of signals (2x7p/3x7q) suggested the presence of the i(7)(q10) and additional structural aberrations involving the second chromosome 7. In two cases, including one alphabeta phenotypic variant, a variety of FISH patterns equivalent to two to five copies of i(7)(q10) or numerical and structural aberrations of second chromosome 7 has been detected. These findings support cytogenetic data pointing to a characteristic association of i(7)(q10) with HSTCL, irrespective of the immunophenotype of malignant cells. An increased number of 7q signals was found in three cases with cytologic features of progression, indicating a tendency of HSTCL to multiply the i(7)(q10) chromosome during evolution. (C) 2002 Wiley-Liss, Inc.