FISH demonstrates treatment-related chromosome damage in myeloid but not plasma cells in primary systemic amyloidosis

Conventional cytogenetic analysis is limited in the evaluation of plasma ce ll disorders because, relative to normal hematopoietic elements. plasma cel ls divide slowly. Moreover, it is difficult to know whether abnormal metaph ases originate from malignant plasma cells or myeloid cells harboring other abnormalities. We studied a patient with primary systemic amyloidosis who had previously been treated with an alkylating agent. Bone marrow cells wer e analyzed by cytoplasmic-immunoglobulin fluorescent staining combined with fluorescent in situ hybridization (cIg-FISH). Both chromosome enumeration probes for chromosome 1 and 7 and loci-specific probes for the short and lo ng arm of chromosome 7 were used. Cytogenetic analysis disclosed the follow ing abnormality: +der(1;7)(q10;p10). On cIg-FISH, the myeloid cells had fus ion signals between chromosome enumeration probes for chromosomes 1 and 7, whereas plasma cells had the normal appearance of two pairs of signals. The re was a second clone of abnormal myeloid cells with monosomy of chromosome 7. The bone marrow did not show any evidence of myelodysplasia. Interphase cIg-FISH is a useful technique for assigning the lineage of chromosomal ab normalities in plasma cell disorders.