This is a clear indication that MDS clones dominate the myeloid lineage. We used a chromosome 9 probe instead and found that almost all the myeloid lineage cells obtained monosomy, which suggests that all the myeloid lineages have already substituted the myeloid lineage cells with two chromosome 9 alleles. The substitution might have occurred because the case's chromosome 9 clone had a growth advantage, dominating the myeloid cell lineage. Alternatively, but not exclusively, the appearance of a morphological abnormality as MDS was a late event in this case and during the preceding unknown time, a clone with normal karyotype might have disappeared. Table 1 .
Control is a bone marrow smear obtained from a normal healthy volunteer.
One hundred cells were counted in the blasts, myelocytes, granulocytes, erythroblasts and myeloma cells. Ten cells were counted in the lymphocytes. We have shown in the present study that erythroid lineages are also substituted by cells with abnormal karyotype. Because the monosomy 9 clone dominated in the present MDS case and erythroid series were relatively abundant, we had a good opportunity to examine sufficient numbers of erythroblasts. Our findings that the multiple myeloma clone did not contain the monosomy 9 MDS clone and that the MDS clone retained the germ line configuration of immunoglobulin gene suggest that the MDS clone and multiple myeloma clone are independent.