Evaluating the utility of K homology domain-containing protein (KOC) in making a distinction between reactive mesothelial cells and metastatic adenocarcinoma in pleural effusion

Background: Distinguishing adenocarcinomas from reactive mesothelial cells in pleural effusion samples is known as an important challenge for pathologists. Here we aimed to assess the effectiveness of K homology domain-containing protein (KOC) marker in this regard. Methods: This is a cross-sectional study that was performed in (XXX) on cell block of 82 pleural effusion samples (41 reactive effusion and 41 metastatic effusion). For selected slides, immunohistochemical (IHC) staining with avidin-biotin method was performed on the prepared sections. We used Rabbit anti KOC L523S antibody for the staining with using positive and negative controls. For evaluation of staining diffuseness, slides were examined first with objective lens 4, x40 magnification to select the appropriate area and then with objective lens 4, x40 magnification in terms of percentage and the samples were classified in terms of staining intensity. Results: 39% and 41.5% of samples in reactive mesothelial cells group had + 1 and + 2 staining diffuseness respectively while 70.7% of samples in the adenocarcinoma had + 3 staining diffuseness (P< 0.001). Furthermore, 46.3% and 39% of cases in reactive mesothelial cells group had weak and moderate staining intensity respectively while 61% and 24.4% of cases in adenocarcinoma group had severe and moderate intensity respectively (P< 0.001). Diffuseness of KOC staining had 70.7% sensitivity and 87.8% specificity and the intensity of KOC staining had 61% sensitivity and 92.7% specificity in differentiation of reactive mesothelial cells and adenocarcinoma. Receiver operating characteristic (ROC) curve showed KOC can discriminate adenocarcinoma with a sensitivity of 70.7% and specificity of 87.8% from reactive mesothelial cells. Conclusions: KOC is an appropriate marker for distinguishing reactive mesothelial cells from metastatic adenocarcinoma in pleural effusion.