Initial molecular and cytogenetic evaluation. (A) Karyogram of G-banded chromosomes reveals an aberrant add(9)(p21.3) in all 20 metaphases and trisomy 19 in 19 of 20 metaphases analyzed (46,XX,add(9)(p21.3)[1]/47,idem,+19[19]). (B) Next-generation RNA sequencing identified an aberrant transcript corresponding to a fusion between exon 4 of ETV6 (upstream) and exon 5 of FGFR2 (downstream). (C-E) FISH with Vysis TelVysion subtelomeric probes post G-banding reveals subtelomeric loss of 9p from the add(9)(p21.3) chromosome (C), abnormal localization of 1 copy of 12p to the short arm of the add(9)(p21.3) chromosome (D), and abnormal localization of 1 copy of 10q to the short arm of the add(9)(p21.3) chromosome (E). (F) FISH with Vysis LSI ETV6(TEL)/RUNX1(AML1) probe set reveals abnormal localization of 1 copy of ETV6 to the long arm of chromosome 10. These findings are favored to represent the sum of the 2 rearrangement events among chromosomes 9, 10, and 12, resulting in the add(9)(p21.3) aberrancy as well as cryptic aberrancies of chromosomes 10 and 12, including abnormal localization of the ETV6 FISH probe to the long arm of chromosome 10. (G-H) The order of these rearrangement events cannot be determined, but 2 speculative hypotheses are proposed. Ig, immunoglobulin.