Abstracts of Clinical Meeting on 12-July-2002
Cytogenetics in Myeloma
Dr Fiona Ross. Director LRF UKMF Cytogenetics Database, Wessex Regional Genetics Laboratory, Salisbury District Hospital, Wilts SP2 8BJ.
A feasibility study funded by the LRF has been used to determine what cytogenetic results could reasonably be expected from patients entered into the Myeloma IX Trial. We have shown that both numerical and structural cytogenetic abnormalities can be easily detected in purified plasma cells from myeloma bone marrows. Sufficient cells can be recovered, even from marrows with only a low percentage of plasma cells, provided that an adequate aspirate is taken.
We have developed a microtechnique for FISH which allows multiple tests to be carried out even when as few as 2 x 105 cells are recovered from purification. 231 patients have so far been checked for chromosome 13 status and the presence of a 14q32 rearrangement. 38% of cases had a deletion of 13 which is in good agreement with other series. However only 40% of cases had a 14q32 rearrangement as a major abnormality. This is well below the 75% expected from the literature.
At present we have two hypotheses which may explain this result. One suggests that the patient group we have tested is in some way different from those in other series, and genuinely has an unusually high proportion of cases without 14q32 abnormality. The other postulates that we are missing a significant proportion of cases due to the large gap between the proximal and distal commercial probes being used.
We have now obtained the same probes as used by the French group who have a 75% 14q32 abnormality rate in more than 900 patients, and are currently retesting our samples with these probes. 14% of the patients had a t(11;14) (cf 16% in the French series) and 6.3% had a t(4;14) (cf 10%). Current published indications are that these may be good and bad prognostic indicators respectively.
We have also been using centromere specific probes as a guide to whether cases have gained or lost chromosomes. 65% of cases appear to be hyperdiploid, 19% hypodiploid and 16% have no evidence of numerical abnormalities for those chromosomes tested. Overall 96.5% of cases studied by FISH have at least one abnormality, a much higher proportion than previously published for this method of detecting abnormalities.
Initial conventional cytogenetic results, predominantly on samples with >15% plasma cells, showed a 19% abnormality rate. However a change in methodology has led to a 26% abnormality rate on all samples, with that for samples with >15% PC being 71%. An abnormal clone has been detected in samples with as few as 1% PC, confirming that proliferation rate rather than absolute cell numbers is probably the limiting factor in obtaining dividing plasma cells. This level of abnormal cases augurs well for finding new abnormalities in myeloma among the trial patients, for whom we have funding to do M-FISH.
The feasibility study has shown that excellent and detailed cytogenetic results can be obtained on essentially all samples containing at least 1 x 106 plasma cells. However, the median number of plasma cells in the 513 samples received from October 2000 to June 2002 was only 1.09 x 106. Thus the major effort for future samples, especially those from trial patients, must be in improving the quality of the aspirate taken for cytogenetics.