Role of Immunohistochemistry in Determining Origin of Metastatic Tumors in Pleural and Peritoneal Effusions

Aim of Study Effusion cytology is a test used to determine the etiology of a disease. Pleural, ascitic, pericardial, synovial, and cerebrospinal fluid are commonly analyzed samples. When a malignancy is detected in effusions, the place of origin cannot be determined merely by cytologic appearance. In the era of advanced technology, cytomorphology alone is insufficient, and hence, immunocytochemistry is the most widely used modality in cytology effusion. Application of judicious immunopanel can help determine origin of metastatic tumor, hence aiding the clinician in initiation of treatment and prompt management of wider spread disease.  Material and Methods It was a single center study carried out at Chugtais Institute of pathology for a period of one year. All malignant pleural and peritoneal effusions from both genders were included in the study. Concomitant naturally formed clots were fixed in 10% neutral buffered formalin and processed as cell blocks. Cell blocks were prepared using the complex streptavadin-biotin peroxidase technique. Immunohistochemistry was applied to 104 cases with external positive controls. CK7, CK20, Wt1, GATA3, Napsin A, CDX2, LCA, PAX8 & TTF1 were applied to determine primary site of origin.  Results Most common cause of malignant peritoneal effusion was due to ovarian malignancies in females and adenocarcinoma in males while, in case of pleural effusion, it was breast carcinoma in females and lung carcinoma in males.  Conclusion Cellblock combined with a judicious immunohistochemical panel according to gender and most common metastatic tumors can be an accurate and affordable method to determine the primary site of cancer. Our study results signifies the necessity of utilizing a panel of markers to prevent misidentification of the primary sites of metastatic carcinoma in effusions.)