FISH Analysis in Multiple Myeloma - a Retrospective Study from India

Introduction

Multiple myeloma (MM) is a malignancy involving terminally differentiated plasma cells. It is characterized by a complex pattern of extensive genomic aberrations involving many chromosomes and it constitutes about 1% of all malignancies. Its exact incidence in India is not known. Based on data available from 6 population-based cancer registries in India (covering 0.3% of the population) its incidence varies from 0.3 to 1.9 per 100 000 for men and 0.4 to 1.3 per 100 000 for women. Among various prognostic markers in MM, cytogenetic abnormality detected by conventional cytogenetic and FISH studies are major factors deciding clinical outcome. Interphase FISH studies from various parts of the world have reported variable incidence (40 - 66%) of cytogenetic abberations. However, there is insufficient published data from Indian subcontinent addressing the frequency of chromosomal aberrations using interphase FISH in MM patients.

Patients and Methods

Sixty eight patients clinically diagnosed with multiple myeloma were studied. The retrospective period of recruitment was from Jan 2015 to June 2016. The diagnosis of MM was based on serum electrophoresis and immunofixation, bone marrow plasmacytosis, and end organ involvement. Interphase FISH analysis was performed on bone marrow samples using specific DNA probes- Del 13q14.3 (LSI D13S25) , t (4;14) ( Kreatech IgH/ FGFR3 DC-DF), t (11;14) (Zytovision directly labeled IgH/CCND1 DC-DF), t (14;16) (Kreatech IgH/ MAF DC-DF), Del 17p13.1( LSI TP53). A total of two hundred nuclei were enumerated for each FISH Panel probe and cut off for detection of deletion/ fusion signal in normal individuals was taken as 3%. An interim analysis of treatment protocols was also done.

Results

A total of 68 cases with MM were evaluated which included 55 males and 13 females. We report a median age of 58 years (37-86 years). Interphase FISH analysis was done in all patients. Out of sixty eight patients, 23 (33.82%) patients had one genetic abnormality. Results revealed that deletion 13q14.3 was the most frequent aberration. Out of 68 patients, 10 patients have 13q14 (14.7%) abnormality. This includes 70% males and 30% females. In addition absence of p53 at 17p13 was detected in 8/68 (11.8%) patients. Similarly 11q13 abnormality was observed in 3/68 (4.4%). IgH (14q32) aberrations were noted in 2/68 (2.94%) patients. Of which t(4;14) was detected in these patients, whereas none of them showed t(14;16). More than one chromosomal aberrations were present in 4 patients. Data for serum β₂-microglobulin at the time of presentation could be evaluated in 52 patients only. Most of the patients 40(76.9%) belonged to ISS stage 3. From the available data, 4 patients with ISS stage 3 had high risk chromosomal abnormality whereas 3 patients with ISS stage 2 and none of the patient of ISS stage I disease had high risk chromosomal abnormality. A total of 40 patients received cyclophosphamide, bortezomib and dexamethasone as the primary treatment whereas 23 patients received Bortezomib, lenalidomide and dexamethasone based therapy. Post 2 cycles of cyclophosphamide based therapy showed an overall response rate (CR + VGPR) of 87.5% whereas in case of lenalidomide based therapy the overall response rate was 91%. Thirteen patients underwent autograft after durable response, out of which one had a clinical relapse within 3 months. Median survival can only be commented on further follow up.

Conclusion

In comparison to the west, the frequency of chromosomal aberrations are different and much less in India whereas the studies of median survival is comparable. An early age of presentation in Indian subcontinent is another issue to be addressed as we know that secondary mutations accumulate with increasing age, but a younger population presenting with same severity of disease needs exploration of additional abnormalities in India. Being a resource constraint country and non availability of molecular lab at every place, evaluation of each patient is difficult, however increasing awareness of the role of biology in the management of MM is inspiring the clinicians for detailed evaluation and close follow up of these patients. Certainly, larger trials are required to understand the biology of this disease in the country.