Brief communications 13 8 9TEE because of artifacts. In urgent circumstances, even if the need to minimize delay appears to justify the desire to reduce the number of studies, reliable information is mandatory. We therefore believe that only highly accurate techniques such as multiplanar TEE should be employed in diagnosing aortic dissections.

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During fluorescence in situ hybridization (FISH) analysis of metaphase cells from 70 patients with lymphoid and myeloid hematologic malignancies and chromosomal rearrangements involving band 12p13, we identified nine patients (four with lymphoid malignancies, four with myeloid malignancies and one with biphenotypic leukemia) who showed more complicated rearrangements than we had expected from conventional cytogenetic study. In six patients, multiple breaks occurred in small segments of 12p with subsequent translocations and insertions of these segments into other chromosomes, sometimes to unexpected regions. In three patients additional chromosome breaks resulted in a sub-clone which was cytogenetically indistinguishable from the main clone in each patient based on the cytogenetic analysis. These subtle molecular events were detected exclusively in a region covering TEL/ETV6 and KIP1/CDKN1B. Seven of nine had a previous history of chemo/radiotherapy; all the patients showed complex karyotypes, even though they were newly diagnosed with leukemia. Survival data were available in five patients, and all survived less than 6 months. These findings suggest that the 12p13 region, especially the above-mentioned region, is genetically unstable and fragile. It is likely that multiple chromosome breaks were induced through mutagens used in chemo/ radiotherapy, and are associated with a sub-group of patients with an extremely bad prognosis. Leukemia (2001) 15, 1193-1202.

Unbalanced translocations as well as interstitial deletions of the short arm of chromosome 12 [del(12p)] are found as recurring chromosomal changes in a broad spectrum of hematopoietic malignancies. These changes result in the hemizygous deletion of genetic material from 12p. We mapped a yeast artificial chromosome containing the TEL gene, a cosmid contig containing part of TEL and a P1 contig containing the KIP1 gene to 12p13. These probes were used for fluorescence in situ hybridization to analyze samples from 47 patients with various hematologic malignancies who had unbalanced translocations (25 patients) leading to loss of 12p or deletions (22 patients) involving 12p13. The patients had acute lymphoblastic leukemia (8 cases), myelodysplastic syndrome (MDS; 11 cases), acute myeloid leukemia (AML; 10 cases), myeloproliferative disorders (4 cases), therapy-related MDS or AML (7 cases), non-Hodgkin's lymphoma (2 cases), and other hematopoietic malignancies (5 cases). All three probes were hemizygously detected in 26 cases and were completely retained in only 9 cases. In 12 cases probes for one of the two genes were deleted, allowing us to map the smallest region of overlap of these deletions to a small genomic region that is bordered on the telomeric side by the TEL gene and on the centromeric side by KIP1. The genomic distance between TEL and KIP1 is estimated to be about 1 to 2 Mbp.