Trisomy 15 is frequently observed as a minor clone in patients with anemia/MDS/NHL and as a major clone in patients with AML

Trisomy 15 as the sole karyotypic aberration is an uncommon clonal cytogene tic aberration in hematological malignancies, making its significance uncle ar. Previous studies have reported relations of trisomy 15 with low-grade m yelodysplasia or a benign age-related phenomenon associated with loss of th e Y chromosome. To define the significance of trisomy 15, we conducted a re trospective study of all examples of trisomy 15 accessed in our laboratorie s. Trisomy 15 was observed asa clonal abnormality (greater than or equal to 2 cells) in 17 cases and nonclonal (single cell) in 9 cases. The majority o f cases (14/17 clonal cases) had a minor clone (5-35% of metaphase cells) o f trisomy 15. The minority of cases (3/17) had a major clone (80-95% of met aphase cells) of trisomy 15. Two of these 3 cases were diagnosed as having acute myelocytic leukemia. Fluorescence in-situ hybridization (FISH) with t he use of a chromosome Is-specific alpha-satellite probe was per-formed on 3 of 17 clonal cases and on 3 of 9 nonclonal cases. FISH results revealed t he presence of a minor clone (from 3 to 5 of 700 interphase cells) in 5 of them, 2 of which had trisomy 15 in 20% of metaphase cells. These results ma y indicate that the 20% of trisomy 15 are very likely on overrepresentation of a very minor clone that could be transitory In summary, the analysis of our cytogenetic and FISH results revealed the presence of two types of tri somy 15 clones: a minor clone that could be transitory or indolent and a ma jor clone that could be of a neoplastic nature. (C) 2000 Elsevier Science I nc. All rights reserved.