Colonic gastrointestinal stromal tumor: A diagnostic dilemma on cytology

Gastrointestinal stromal tumors (GIST) is mesenchymal tumors arising from the interstitial cells of Cajal (pace maker cells) of the gastrointestinal tract (GIT). Stomach is the most common site (60-65%) of these tumors. Large intestine and rectum constitute only 5-10% of GIT tumors. Pre-operative diagnosis helps in the management of this tumor as it responds well to c-kit inhibitors. The cytological diagnosis of GIST is characteristic, however, associated with many pitfalls leading to erroneous diagnosis. Morphological resemblance is seen with other spindle cell and epithelioid cell tumors. The differentiation between high grade and low grade GISTs is described but not reliable. Cytology combined with cell block and Immunocytochemistry helps in making a confident diagnosis. Here we present colonic GIST diagnosed as GIST on cytology and confirmed on histopathology. We report this case to describe the cytological features of GIST and pitfalls in the cytology.