Abstract Poorly differentiated carcinoma of lung is a very aggressive tumor. It lacks typical morphological and architectural features posing great diagnostic difficulties. Diagnosing cells as being ‘reactive mesothelial cells’, benign or malignant in effusions is a common diagnostic difficulty on conventional smear(CS) examination. Cell blocks(CB) are valuable when the cytological features on CS examination are inconclusive. The main advantage of CB technique is obtaining multiple sections for special stains and immunohistochemistry(IHC). CB technique also offers many other advantages like better preservation of architectural features, cytoplasmic and nuclear details. Coupling CB with IHC not only helps to detect the tumor-type but it also pin points the unknown primary site in cases especially unfit for surgery/biopsy. We report a case of 70yr non-smoker female known case of Ischemic Heart Disease (IHD). She presented with breathlessness, chest pain and recurrent pleural effusions since last 2 months.

Keywords: Cell block, Conventional smear, Immunohistochemistry, Malignant effusion.