FISH Reveals Abnormalities of Unsuspected Regions in Chromosomally Normal De Novo Myelodysplastic Syndromes (MDS).

Abstract 2599

Poster Board II-575

In de novo MDS the chromosomal pattern is a mandatory step for an accurate diagnosis, predicts overall survival (OS) and the risk of MDS/AML evolution, guides therapeutic decisions. However, conventional cytogenetics (CC) studies show a normal un-informative chromosomal pattern in about half of MDS patients, especially in low-risk disease. FISH with probes pinpointing the chromosomal regions most frequently affected in MDS can increase the incidence of abnormal karyotypes up to 60%, but the percentage of normal karyotypes remains high and makes the search of novel cytogenetic/molecular markers a urgent need. A fundamental contribution to overcome CC and FISH shortcomings, has been recently provided by array CGH (aCGH) studies which have revealed that, independently of the cytogenetic pattern, MDS patients may harbour novel abnormalities involving unsuspected chromosomal regions.

Based on this assumption, we decided to investigate whether FISH with probes already employed in aCGH studies can truly unmask cryptic lesions in chromosomally normal MDS patients, whether these defects are either chromosomal gains/losses or balanced rearrangements and whether these chromosomal abnormalities influence OS and disease evolution. FISH analyses were carried out in thirty-five patients examined between January 2005 and June 2008. There were thirteen females and twenty-two males, whose median age was 66 years (range 24–78). According to WHO classification, 6 patients were classified as RA, 13 as RAEB-1 and 16 as RAEB-2. According to IPSS score, 7 patients were considered low-risk, 14 intermediate-1 risk and 14 intermediate-2 risk. Median follow-up was nine months (range 1–46). At the time of the analyses no patients has died; 6 have progressed to RAEB-2 and 3 to AML. Probes for FISH analysis were chosen following two criteria: the frequency of their involvement in chromosomal abnormalities identified by aCGH studies and their Mb position on Human Mar. 2003 assembly according to the UCSC genome browser. All probes, obtained from BACPAC Resources Center at C.H.O.R.I. (Oakland, USA), were labelled and applied as previously reported. The following probes were applied: RP11-912d8 (19q13.2); RP11-196p12 (17q11.2); RP11-269c4 (14q12); RP11-351o1 (10q21.3); RP11-144g6 (10q11.2); RP11-122a11 (7q34); RP11-951k18 (5q13.1); RP11-100m20 (4p14); RP11-544h14 (2q33). The cut-off values for interphase FISH (i-FISH) were obtained from the analysis of 300 nuclei from ten normal samples and were fixed at 10%. An abnormal FISH pattern was revealed in eighteen patients (51.4%). It was observed in 3/6 RA patients, in 7/13 RAEB-1 and in 8/16 RAEB-2 and in 2/7 IPSS low-risk, in 7/14 intermediate-1 risk and in 9/14 intermediate-2 risk MDS patients. Seven presented a 19q13.2 deletion, three a 14q12 deletion, four an amplification of band 4p14, two a defect of band 10q21.3, two a potential amplification and one a deletion of band 10q11.2, two a deletion of band 5q13.1 and one a deletion of band 17q11.2. Cryptic defects were also revealed in six of the nine patients who experienced disease evolution on FISH analyses. This event occurred in 2/3 RA, in 2/7 RAEB-1 and in 2/8 RAEB-2 patients with an abnormal FISH pattern. Despite these data, the prognostic significance of an abnormal FISH pattern needs to be assessed on additional patients.

In conclusion, our data show that i) FISH can truly reveal novel lesions involving unsuspected chromosomal regions in 51% of MDS patients with a normal karyotype; ii) most of these lesions consist of chromosomal gains/losses; iii) an abnormal FISH pattern seems to correlate with disease progression, but this correlation needs to be tested on additional patients.