Deletions of the long arm of chromosome 13 (13q-) have been observed in the clonal plasma cells (PC) of a large proportion of multiple myeloma (MM) patients. Studies of the prevalence and nature of 13q- have been confounded by the inclusion of patients with prior exposure to therapy, lack of selection of PC for scoring (by enrichment or immunofluorescence), or use of single probes or probes in combinations with invalid controls. No good centromeric probe is available for the study of chromosome 13 ploidy. To better understand the molecular cytogenetic nature of 13q- in MM we studied a cohort of 351 MM patients, entered into the clinical trial E9487. We used FISH with the probes LSI 13 (that includes Rb) and D13S319 (Vysis, Inc.) to study the 13ql4 region, in combination with immunofluorescent detection of the clonal PC. Two independent-blinded scorers, who aimed at counting 100 PC, scored all slides. We also studied a representative sample of 80 patients from the original cohort; 40 with and 40 without evidence of 13q 14 deletion for deletions telomeric to 13ql4. We used the probe D13S25 (Vysis, Inc.) and a 13q sub-telomeric BAC clone (Genome Systems, BAC Human Release II) obtained using PCR primers for the marker D13S327 (GDB: 229252). Of 351 patient samples 325 patients could be analyzed (failure rate 8%) with 176 showing evidence of deletions of 13ql4 (54%). In most cases there was simultaneous loss of a pair of LSI 13/D13S3I9 probes, with no cases of nullisomy observed, and only rare trisomy. Of 40 cases with evidence of 13ql4 deletions 34 also showed simultaneous loss of the pair of probes D13S25 and BAC D13S327 (85%) thus indicating monosomy, and in 6 cases D13S25 was missing but D13S327 was conserved indicating an interstitial deletion involving I3ql4 (15%). Among 40 patients with a normal LSI 13/D13S319 pattern 39 also had preserved signals for the probes D13S25/D13S327 (97.5%) and only one showed an extra signal of D13S327 indicating a possible trisomy with an interstitial deletion (2.5%). Deletions of 13ql4 are common in untreated MM. Our data support that 13q- deletions are usually large deletions of that involve all of 13q initiating at least at q!4 - if not signalingmonosomy.
|Original language||English (US)|
|Issue number||11 PART I|
|State||Published - Dec 1 2000|