Multiple myeloma; extramedullary relapse; clonal evolution; genetic changes; ploidy switch; TP53 mutations

Extramedullary relapse (EM) is an aggressive form of the disease with a dismal outcome. We present cytogenetic findings of a 52-year-old female with MM, which progressed rapidly into plasmocellular leukemia and extramedullary subcutaneous tumor in the head. At the time of diagnosis, G-banding showed hypotriploid karyotype (63-64 chromosomes) and using cIg-FISH we found translocation t(4; 14)(p16; q32) and gain(1)(q21). At the time of disease progression, the same chromosomal abnormalities were present in the bone marrow, peripheral blood and the EM lesion: del(13)(q14), del(17)(p13), t(4; 14)(p16; q32) and gain(1)(q21). Before progression, array-CGH showed, hyperdiploid karyotype with trisomies of chromosomes 2, 3, 7, 8, 9, 11, 17, 18, 19 and 20, while after progression non-hyperdiploid karyotype was detected with additional structural deletions in 1p, 2p, 4q, 11p, 12p, 13, 14q, 17p, 22q and homozygous deletion in 1p32.3. In addition, deep resequencing of TP53 gene showed presence of 2 known mutations in exon 6(c.632C>T) and exon 7(c.700T>C). In summary, EM relapse of this patient was connected to a change of the entire genome profile. Extramedullary lesion most probably originated by an expansion of one clone of tumor plasma cells from the bone marrow, which was confirmed by identical genomic profile of both tested samples. Thus, change of ploidy status should be considered as potential hallmark of adverse course of the disease.