[Histological and molecular analysis of brain metastases]

The first step in the diagnosis of a metastatic brain lesion is to exclude a primary central nervous sytem tumour, followed by verification or identification of the primary tumor site, in order to guide the clinician to specific therapy. In addition to morphological features, ancillary immunohistochemical study is most effective for the evaluation of a metastatic neoplasm of unknown primary. Although the main principles are same, there are slight variations in the approach to the secondary lesion in the central nervous system versus other regions. Indeed, immunohistochemical approach focuses on the most common tumor types associated with secondary brain colonization: lung cancer, breast cancer and melanoma. Several studies have reported that targeted therapies are capable of reducing brain metastases in melanoma or non-small cell lung cancer, sometimes with a high dramatic response. These results have clearly impacted routine neuropathological practice. It is likely that molecular subtyping of central nervous system metastases will play an increasing role in the future. In accordance with the recommendations of Inca (French national cancer institute), the pathologist develops appropriate strategies for molecular and immunohistochemical analysis, in order to provide results as soon as possible. This article summarizes the diagnosic approach to brain metastases, with a focus on the recent emergence of targeted therapies.