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 cytogenetic aberration in hematological malignancies, making its significance unclear. Previous studies have reported relations of trisomy 15 with low-grade myelodysplasia or a benign age-related phenomenon associated with loss of the Y chromosome. To define the significance of trisomy 15, we conducted a retrospective study of all examples of trisomy 15 accessed in our laboratories. Trisomy 15 was observed as a clonal abnormality ( ≥2 cells) in 17 cases and nonclonal (single cell) in 9 cases. The majority of cases (14/17 clonal cases) had a minor clone (5–35% of metaphase cells) of trisomy 15. The minority of cases (3/17) had a major clone (80–95% of metaphase cells) of trisomy 15. Two of these 3 cases were diagnosed as having acute myelocytic leukemia. Fluorescence in-situ hybridization (FISH) with the use of a chromosome 15-specific alpha-satellite probe was performed on 3 of 17 clonal cases and on 3 of 9 nonclonal cases. FISH results revealed the 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 may indicate that the 20% of trisomy 15 are very likely an 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 trisomy 15 clones: a minor clone that could be transitory or indolent and a major clone that could be of a neoplastic nature.