Circulating microRNAs as prognostic therapy biomarkers in head and neck cancer patients

Squamous cell carcinomas represent the most common malignancies of the head and neck region. About two-thirds of patients with head and neck squamous cell carcinoma (HNSCC) exhibit advanced stage disease, usually involving regional lymph nodes (Argiris et al, 2008). Advanced HNSCC have often a poor prognosis despite intensive local treatment due to tumour recurrences and distant metastases. About 50–60% of patients with advanced disease develop local or regional recurrences after treatment (Hoffmann, 2012). Known risk factors for the development of HNSCC are tobacco use and alcohol consumption (Blot et al, 1988; Tuyns et al, 1988), as well as human papillomavirus (HPV) infection, mainly type 16, which particularly increases the risk for tonsillar and oropharyngeal cancers (D'souza et al, 2007). Human papillomavirus-positive HNSCC tumours have a favourable prognosis (Licitra et al, 2006; Bledsoe et al, 2013) and show a better therapy response (Argiris et al, 2008). Thus, HPV status represents a valuable predictive biomarker that should be taken into consideration for treatment planning to prevent excessive therapy. To date no biomarker for therapy monitoring or patient surveillance is established. Predictive biomarkers in the peripheral blood, such as the newly identified marker HSP70 in HNSCC patients (Gehrmann et al, 2014), provide a minimally invasive way to predict therapy outcome. Recently, it was shown that microRNAs (miRNAs) in plasma samples exhibit high stability and are resistant to RNase activity (Mitchell et al, 2008). This stability combined with the good accessibility make circulating miRNAs attractive biomarker candidates. MiRNAs represent a class of promising biomarkers in cancer research since they are highly specific and are associated with pathoclinical parameters of the disease (Sethi et al, 2013). They can have protective or carcinogenic effects by post-transcriptional regulation of either tumour suppressor genes (Zheng et al, 2011) or oncogenes (Nohata et al, 2011). Since miRNAs are part of the cellular stress response they bear a high potential for diagnostic and prognostic use in cancer patients (Li et al, 2009). The aim of the present study was to evaluate blood plasma miRNAs as minimally invasive biomarkers for radiotherapy monitoring and prognosis. For this purpose, we used a cohort of HNSCC patients with locally advanced and unresectable tumours undergoing radiochemotherapy or radiotherapy alone, which is the common treatment for these cases (Adelstein et al, 2003). We previously analysed the therapy effect on the plasma miRNAs by comparing the miRNA profiles in plasma of HNSCC patients before therapy and after the completion of the first two fractions of therapeutic irradiation (Summerer et al, 2013). MiRNAs showing changed levels were tested in the present study to determine their prognostic value and their potential for predicting the individual tumour response to radio(chemo)therapy. For this purpose, we tested the expression levels of the miRNAs for their correlation with locoregional tumour control (LRC), progression-free survival (PFS) and overall survival (OS). To check for a possible tumour origin of the therapy-regulated plasma miRNAs, we compared miRNA levels in plasma samples from HNSCC patients prior to treatment with an age- and sex-matched group of healthy donors. MiRNAs that were identified as patient-specific markers or as therapy-responsive miRNAs were validated in an independent HNSCC patient cohort. To further support the hypothesis that the detected alterations in plasma miRNAs are tumour related, we analysed tumour biopsies from the same patient cohorts.