An Interphase Chromosome Profiling Assay to Determine the Need for CD 138 Enrichment in the Genetic Workup of Multiple Myeloma

Plasma cell neoplasm, a B-cell malignancy is very common in elderly population and is currently incurable despite multiple treatment strategies. Genetic characterization, especially karyotype plays an important role in the diagnosis, prognosis as well as in the follow-up during treatment. In general, plasma cells are non-dividing and don't cooperate in tissue culture and as a result, over 90% of all standard cytogenetic studies end up having a "normal" karyotype. FISH testing using several probes has proven very useful in detecting the clonal abnormalities.

It has been suggested and some laboratories do use CD138 antibodies to enrich the plasma cells in an effort to increase the detection rate of clonal abnormalities. However this additional step adds cost to the overall testing and the efficacy of this enrichment and the clinical utility is somewhat controversial. Many institutions don't enrich the plasma cells and still can detect the clonal abnormalities using FISH probes. It would be of interest if the need for enrichment is clarified and if the results from un-enriched studies are comparable to those of enriched, then the cost savings will be obvious.

FISH testing, while extremely useful in increasing the detection of clonal abnormalities on the "normal" cytogenetic samples, has limitations in the sense that it can only detect the common changes targeted in the panels. Approximately 25% of all abnormal cases do have complex karyotypes harboring changes both numerical as well as structural that are beyond the scope of detection utilizing the current FISH panel of probes. These additional clonal changes have prognostic significance and it is well established that the greater the complexity of the karyotype, the worse is the prognosis. Therefore, it is imperative, from a clinical management standpoint that the testing laboratories use technologies that will detect all chromosomal abnormalities given the dismal culture success rate of traditional cytogenetic methods in detecting the abnormal clones.

We have recently developed and validated a novel technology termed "Interphase Chromosome Profiling" (ICP) (Cytogenet Genome Res 2014;142:226, Abstract #22) which detects all chromosome abnormalities including the characterization of marker chromosomes and material of unknown origin i.e., add, in karyotypes. We utilized this technology on 10 unenriched samples from patients clinically suspected of multiple myeloma/plasma cell neoplasm. Each case had the traditional karyotype and FISH studies, in addition to ICP. Seven of the ten had a normal result with cytogenetics and FISH. ICP also produced a normal result in these cases. Three cases had an abnormal result by Cytogenetics and FISH. One of them had only one cell with abnormalities in the cytogenetic study. All three had complex karyotypes harboring the classic numerical abnormalities characteristic of multiple myeloma such as trisomy for chromosomes 3, 5, 7, 9, 11 etc. as well as multiple structural abnormalities including marker chromosomes and extra material of unknown origin (add). FISH failed to identify many of these structural changes which is an inherent limitation of the current design of panel of probes in clinical use. ICP on the other hand, detected not only all the abnormalities identified by both cytogenetics and FISH, but clarified and/or characterized the marker chromosomes and "add"s in these complex karyotypes. Interestingly, ICP identified a NOVEL duplication of the long arm of chromosome X, dup(X)(q21.3qter) in two of the three abnormal cases. Review of the literature indicates that this duplication on X chromosome is found in 20% of cases and harbors Cancer/Testis Antigens (CTAs) belonging to the MAGE family (CTA-X-MAGE) (Clin Dev Immunol. 2012;2012:257695. doi: 10.1155/2012/257695. Epub 2012 Mar 11) and is a potential target for novel immunotherapies. Yet classical cytogenetic approaches including FISH on enriched or unenriched samples will fail to identify this very important and common abnormality for which there is a potential therapy.

Our results strongly indicate that ICP is very sensitive technique and can identify all chromosome abnormalities in interphase nuclei regardless of enrichment procedures for samples from multiple myeloma patients.