[RET rearrangements in advanced lung cancer: a target to always look for.]

Introduction . RET rearrangements have been recently aroused growing interest, due to the availability of target therapies increasingly active and safe. The search for these oncogenic alterations in patients with advanced lung adenocarcinoma has become an integral part of the biomolecular tumoral assessment, in order to possibly provide a selective therapeutical option also for rare subgroups of patients, but belonging to lung cancer that is considered a "big killer", representing the most frequent cause of cancer-related death worldwide. Following to the introduction of modern biomolecular techniques, such as the comprehensive genome profiling (CGP), that has been added to the immunohistochemistry (IHC) and the "in situ fluorescent ibridation" (FISH), the availability of techniques based on genomic sequencing such as the next generation sequencing (NGS), achievable either on tumoral tissue or on plasma, has made it easier to identify oncogenic alterations that, although rare, are potentially treatable with molecularly targeted drugs. A complete molecular assessment should preferable be obtained at the first diagnosis, in order not to neglect the possibility of using target drugs if indicated, but it is possible and desiderable to complete or to re-determine the biomolecular profile also during the clinical course, due to the possibility of spontaneous or drug-induced resistance mechanisms that can modify the biomolecular tumoral characteristics; this reassessment is achievable both through tissutal rebiopsy and by plasma test, the so-called "liquid biopsy". Clinical case . In this report, we describe the case of a patient with advanced lung adenocarcinoma, pretreated with multiple chemo- and immuno-therapic lines of treatment; at baseline, the biomolecular profile was not complete, as well as during the clinical course through repeated re-biopsies. Conclusions . At the time of further disease progression, a liquid biopsy with NGS revealed the presence of a RET rearrangement. This clinical case underscores the importance of a complete biomolecolar assessment in order to identify target linked to effective and innovative treatment options; it is also highlighted the usefulness of the modern CGP techniques, applicable to tumoral tissue and plasma.