Polysomy 13 with Concomitant Deletion of 13q13–14 Involving the Retinoblastoma Gene and the D13S25 Locus in a Case of Acute Myeloid Leukemia

We herein describe a case of acute myeloblastic leukemia (AML), FAB subtype M4, with an unfavorable clinical course and a complex karyotype, including 4–9 copies of chromosome 13. Polysomy 13 was a result of clonal evolution. Fluorescence in situ hybridization (FISH) revealed a cytogenetically unrecognizable deletion within 13q13–14 that included the retinoblastoma gene (RB) and the D13S25 locus in all but one copy of chromosome 13. The only chromosome 13 that did not show a deletion affecting the q13–14 region was translocated to chromosome 7, resulting in a dic(7;13)(q21;p11). In this case, the coexistence of polysomy and a partial deletion within the same chromosome point toward a possible formation of a fusion product with oncogenic potential and its consecutive amplification as a critical alteration in this case.