[RNAseq in routine oncology]

High throughput RNA sequencing, also know as RNAseq, can easily be performed on the gold-standard technique of formalin-fixed paraffin-embedded tissue, which has long been successfully used in routine practice by pathologists. For this reason, RNAseq has been fully adopted in a very short period of time in most French molecular platforms of cancer genotyping, generating "high throughput" data, both qualitative (mutations, fusions) and quantitative (gene expression profiles). This technique opens new perspectives in oncology practice: from a diagnostic point of view (some gene fusions are specific of some diagnoses, some transcriptomic signatures suggest some types of cancer), but also from a prognostic point of view (gene expression profile of an aggressive tumor, or conversely of an indolent one), and above all from a predictive point of view, guiding the choice of potential targeted therapies (example of ALK, ROS1 or NTRK translocations). This technical approach has many advantages, first and foremost it detects, at one go, a plethora of molecular alterations which were previously analyzed sequentially using heterogenous assays (immunohistochemistry, DNA genotyping, fluorescent in situ hybridization, etc.). However, it also presents several drawbacks which may easily be overcome if certain pre-analytic parameters are correctly controlled, mainly aiming at the preservation of the quality of nucleic acids. In any event, the widespread use of RNAseq has had a profound impact on the algorithms of tumor tissue processing, shaping a new, holistic era in oncology.