Apart from our recently obtained findings, four independent studies have thus far been performed to evaluate the predictive/prognostic impact of HOTAIR genomic or/and transcriptomic level(s) on the peripheral blood of breast cancer patients. In 2016, an article was published in the “Thoracic Cancer” journal suggesting overexpression of HOTAIR in circulating peripheral blood of breast cancer patients. Nevertheless, accuracy of this experiment could not be truthfully validated, regarding the wrongly highlighted primers utilized for the evaluation of HOTAIR expression level [2].
On April 2015, findings published in the “Journal of Translational Medicine” suggested up-regulation of HOTAIR expression in the breast cancer tissues and cell lines, through inhibiting miR-148 by estrogenic GPER signalling activity. This article also indicated overexpression of HOTAIR in the patients’ peripheral blood mononuclear cells [3]. Later, another investigation, published in the journal of “Cancer Biomarkers” on May 2018, also suggested positive association of circulating HOTAIR expression with tumour size, positive lymph node quantity and farther metastasis location [4]. Findings obtained from these studies raised the curiosity to navigate the cause(s) of this inconsistency on the mode of HOTAIR expression in the breast cancer patients’ circulating and peripheral blood mononuclear cells compared to the observed results in our experiment. Analysing the latter two experiments showed that similar to our experiment, the allocated HOTAIR primers could anneal both DNA and cDNA molecules, while no DNase treatment has been reported following the isolation of total RNA from the implicated samples. In this case, the data obtained from qRT-PCR would consequently represent combination of both genomic and transcriptomic HOTAIR levels and they could not realistically signify the HOTAIR circulatory or mononuclear cell RNA level in peripheral blood.
On the other hand, another original article was published on July 2015 in the “Breast Cancer Research and Treatment” journal suggesting HOTAIR circulatory DNA as a predictive/prognostic breast cancer biomarker. In this experiment, DNase I was utilized to evaluate RNA expression level of HOTAIR. Additionally, to evaluate genomic copy number of HOTAIR, RNA was not reverse transcribed. Findings showed no significant expression level of HOTAIR transcription, while HOTAIR circulatory DNA was almost duplicated in the serum of breast cancer patients compared to the normal individuals [5]. These findings are somehow in line with our finding, showing low expression level of HOTAIR. Curiously, analysing the data from the “Expression Atlas Biobank of European Bioinformatics Institute” also proposed no significant to very low HOTAIR transcript level in not only normal individuals’ but also breast cancer patients’ peripheral blood [6, 7].