**5. Conclusion**

of genes that are located in their genomic proximity [95]. On the other hand, trans-lncRNA regulate expression of distant genes [100]. Many lncRNA are transcribed by RNA polymerase II, just like protein-coding genes. If lncRNA are involved in the regulation of RNA polymerase II, they are transcribed by RNA polymerase III [87, 101–103]. High degree of evolutionary conservation, tissue-specific expression and stability of lncRNA point to significant functional

Dysregulation of lncRNA expression was observed in various human diseases, including cancer. LncRNA may be either oncogenes or tumor suppressors in development as well as progression of tumors [105, 106]. Changes of expression levels of several lncRNA have been reported in several malignancies; other lncRNA seem to be specific for a single tumor, suggesting that these molecules may be good biomarkers for tumor diagnostics as well as prog-

Moreover, it was shown that lncRNA are involved in regulation of hematopoiesis, including proliferation, differentiation and apoptosis of hematopoietic stem cells as well as progenitors and precursors of mature blood cells [108, 109]. Dysregulated expression of lncRNA was reported in lymphomas, leukemias and MM. It seems possible that expression profile of these lncRNA could have a potential clinical significance in diagnostics and prognostics of hema-

Current information about the role of lncRNA in pathogenesis of MM is very limited. So far, MALAT1 has been described as a marker of early progression [110]. Expression level of this lncRNA was increased in BM cells of newly diagnosed MM patients and changed during progression of the disease. Patients with lower levels of MALAT1 had a higher risk of early progression. Handa et al. showed higher expression level of MALAT1 in MM patients in comparison to MGUS and HD [111]. These results are in correlation with another study of Ronchetti et al. who showed dysregulation of 31 lncRNA, including MALAT1, in MM patients [112]. Moreover, this lncRNA may be important in MM pathogenesis through activation of TGF-β,

An earlier study showed decreased expression of MEG3 in MM patients [114]. Decreased expression or loss of this lncRNA seems to be important in various types of human tumors [115]. In a study by Benetatos et al., MEG3 was reported to be lost in more than half of MM

Our own study showed that UCA1 might be a marker of MM when HD, MGUS and MM plasma cells were compared (with sensitivity of 85.0% and specificity of 94.7%). UCA1 levels seemed to correlate with albumin and monoclonal immunoglobulin serum levels, cytogenetic

Similar to circulating miRNA, even lncRNA may be detected in body fluids suggesting their possible role as biomarkers for diagnosis, prognosis and prediction. They were found in PB

role of these molecules [104].

76 Liquid Biopsy

nosis and prediction [107].

tologic malignancies.

a factor important for osteolytic lesion formation [113].

aberrations, and survival of MM patients.

*4.3.1. Circulating lncRNA*

patients, and it seemed to have a prognostic significance for MM [116].

While not many studies have been published dealing with liquid biopsies of circulating molecules in multiple myeloma, they show a great promise. Liquid biopsies could be used as an adjunct to standard BM biopsy for disease monitoring to enable obtaining more complex results and easier follow-up of patients. While there are many candidate molecules that have been described in this review (cfDNA, miRNA and lncRNA), more studies are needed to validate these findings.
