Real-World Diagnostic Accuracy and Use of Immunohistochemical Markers in Lung Cancer Diagnostics.

objectivesAccurate and reliable diagnostics are crucial as histopathological type influences selection of treatment in lung cancer. The aim of this study was to evaluate real-world accuracy and use of immunohistochemical (IHC) staining in lung cancer diagnostics. MATERIALS AND

methodsThe diagnosis and used IHC stains for small specimens with lung cancer on follow-up resection were retrospectively investigated for a 15-month period at two major sites in Sweden. Additionally, 10 pathologists individually suggested diagnostic IHC staining for 15 scanned bronchial and lung biopsies and cytological specimens.

resultsIn 16 (4.7%) of 338 lung cancer cases, a discordant diagnosis of potential clinical relevance was seen between a small specimen and the follow-up resection. In half of the cases, there was a different small specimen from the same investigational work-up with a concordant diagnosis. Diagnostic inaccuracy was often related to a squamous marker not included in the IHC panel (also seen for the scanned cases), the case being a neuroendocrine tumor, thyroid transcription factor-1 (TTF-1) expression in squamous cell carcinomas (with clone SPT24), or poor differentiation. IHC was used in about 95% of cases, with a higher number of stains in biopsies and in squamous cell carcinomas and especially neuroendocrine tumors. Pre-surgical transthoracic samples were more often diagnostic than bronchoscopic ones (72-85% vs. 9-53% for prevalent types).

conclusionsAlthough a high overall diagnostic accuracy of small specimens was seen, small changes in routine practice (such as consequent inclusion of p40 and TTF-1 clone 8G7G3/1 in the IHC panel for non-small cell cancer with unclear morphology) may lead to improvement, while reducing the number of IHC stains would be preferable from a time and cost perspective.