The blood-borne miRNA signature of lung cancer patients is independent of histology but influenced by metastases

Petra Leidinger 0 Christina Backes Michael Blatt Andreas Keller Hanno Huwer Philipp Lepper Robert Bals Eckart Meese 0 0 Department of Human Genetics, Medical School, Saarland University , Building 60, Homburg/Saar 66421 , Germany Objectives: In our previous studies we reported a panel of 24 miRNAs that allowed discrimination between blood of lung tumor patients independent of the histological subtype and blood of healthy controls with an accuracy of 95.4% [94.9%-95.9%]. Here, we now separately analyzed the miRNA expression in blood of non-small cell lung cancer (NSCLC), including squamous cell lung cancer and adenocarcinoma, and small cell lung cancer (SCLC) patients. Patients and methods: In total, we examined the expression levels of 1,205 miRNAs in blood samples from 20 patients from each of the three histological groups and determined differentially expressed miRNAs between histological subtypes and metastatic and non-metastatic lung cancer. We further determined the overlap of miRNAs expressed in each subgroup with the 24-miRNA signature of lung tumor patients. Results: Based on a raw p-value < 0.05, only 18 blood-borne miRNAs were differentially expressed between patients with adenocarcinoma and with squamous cell lung carcinoma, 11 miRNAs between adenocarcinoma and SCLC, and 2 between squamous cell lung carcinoma and SCLC. Likewise, the comparison based on a fold change of 1.5 did not reveal major differences of the blood-borne miRNA expression pattern between NSCLC and SCLC. In addition, we found a large overlap between the blood-borne miRNAs detected in the three histological subgroups and the previously described 24-miRNA signature that separates lung cancer patients form controls. We identified several miRNAs that allowed differentiating between metastatic and non-metastatic tumors both in blood of patients with adenocarcinoma and in blood of patients with SCLC. Conclusion: There is a common miRNA expression pattern in blood of lung cancer patients that does not allow a reliable further subtyping into NSCLC or SCLC, or into adenocarcinoma and squamous cell lung cancer. The previously described 24-miRNA signature for lung cancer appears not primarily dependent on histological subtypes. However, metastatic adenocarcinoma and SCLC can be predicted with 75% accuracy. - Background Lung cancer is worldwide the leading cause of cancer related deaths in both men and women with estimated 1,608,055 (12.72%) new cases and 1,376,579 (18.2%) cancer deaths in 2008 ([1] available from: http://globocan. iarc.fr, accessed on 09/01/2013). Primarily, lung cancer is divided into two main histological subtypes depending on their cells of origin. Non-small cell lung cancer (NSCLC) account for about 80% of all lung cancers and are further divided by their origin into adenocarcinoma (Adeno-Ca, about 40%), squamous cell carcinoma (sqCLC, about 30%) and large cell carcinoma (about 9%). Small cell lung cancer (SCLC) is far more aggressive than NSCLC and accounts for about 15% of all lung cancers. The classification into the different histological lung cancer types plays a prominent role in clinical management and prognosis of the disease [2]. As most SCLC have spread to other parts of the body at the time of diagnosis surgery is often ineffective, but they respond well to chemotherapy and radiation. For early stage I and II NSCLCs, surgery is the treatment of choice. However, as these two stages combined account for only 25 to 30% of all patients with lung cancer the most common treatment is systemic therapy (chemo- or targeted therapy) and/or radiotherapy [3-5]. Among NSCLCs, adenocarcinoma and squamous cell carcinoma differ with regards to the clinical management and the prognosis. Adenocarcinoma are, for example, more likely to metastasize to the lymph nodes and the brain than squamous cell lung cancer [6]. Lung cancer diagnosis and subclassification is normally based on light microscopic criteria but an accurate diagnosis of histological lung cancer subtypes is often hampered by small tissue biopsies and high observer variability [7-9]. Since several years, microRNAs (miRNAs) have shifted more and more into focus as cancer biomarkers. MiRNAs are small non-coding RNA molecules that are involved in many physiological and pathological processes due to their ability to regulate the expression of most human genes. In the recent past, it was shown that miRNAs are tissue specific and suitable to classify human cancers [10,11]. Especially for lung cancer it was recently shown that classification of different subtypes due to the miRNA expression pattern is possible [12-15]. While these studies were done on lung cancer tissue or cells, there is an increasing number of investigations on miRNAs in the circulation as potential biomarkers [16-27]. In our previous studies, we were able to show that blood-based miRNA expression profiles differentiate between lung cancer patients, patients with COPD and healthy individuals [24,2 (...truncated)