Non-small cell lung carcinoma (not otherwise specified) rates are not solely influenced by pathologists' decisions on the use of immunohistochemistry.

With increasing focus on the molecular classification of non-small cell lung cancers (NSCLC) to guide therapeutic decisions the correct application of appropriate diagnostic tools is paramount. In small biopsy and cytology specimens the majority can be accurately subtyped on their morphological appearances or with the use of additional immunohistochemistry (IHC), namely thyroid transcription factor-1 (TTF-1) and p63 and/or p40.1 Despite this, there is still a small proportion in which sub-classification is not possible therefore the category “not otherwise specified” (NSCLC-NOS) remains valid. This can be the result of a ‘null’ IHC phenotype but can also occur in specimens where there are poorly differentiated malignant cells but insufficient material for subsequent IHC. This article is protected by copyright. All rights reserved.