cIMPACT-NOW update 1: Not Otherwise Specified (NOS) and Not Elsewhere Classified (NEC)

Excerpt

cIMPACT-NOW (the Consortium to Inform Molecular and Practical Approaches to CNS Tumor Taxonomy– Not Official WHO) was established to provide a forum for evaluating and recommending proposed changes to future central nervous system (CNS) tumor classifications [1, 2]. While it is understood that the major impact on international brain tumor classification comes about through the World Health Organization (WHO) classification update process, it is anticipated that this additional process will “see impact” in selected tumor types and in time periods between WHO classification updates. The cIMPACT-NOW (cIMPACT for short) updates can thus provide possible recommendations for practicing diagnosticians and for future WHO classification updates. Since its creation in 2016, cIMPACT has convened three working committees to address current classification and grading challenges. Working Committee 3 addressed questions concerning the use of NOS (Not Otherwise Specified) diagnoses and clarified diagnostic criteria for two entities. The present correspondence reports the recommendations of Working Committee concerning the use of NOS diagnoses, introduces the term NEC (Not Elsewhere Classified), and clarifies the distinction between NOS and NEC when used for CNS tumor diagnosis. …