A Case of Synchronous Diffuse Large B Cell Lymphoma and Gastrointestinal Stromal Tumour.

The occurrence of gastrointestinal stromal tumours (GIST) synchronous with lymphoma is rare. The diagnosis may be overlooked if the lesion is mistaken for the same primary pathology. We report the case of a 66-year-old man who presented with a swelling of the left parotid gland for six months. Histopathology of the parotid gland revealed diffuse large B-cell lymphoma (DLBCL), activated B-cell subtype. Staging positron emission tomography with fluorodeoxyglucose (FDG) and computed tomography (PET-CT) revealed a hypermetabolic left intraparotid lesion, a hypermetabolic mass at the lesser curvature of the stomach with enlarged cervical and bilateral inguinal nodes. Given the persistent FDG avidity on interim PET/CT, fine needle aspiration cytology of the gastric mass with endoscopic ultrasound was performed, confirming GIST. In summary, it is important to recognise patterns of discordant response to treatment leading to re-evaluation of the diagnosis. Early diagnosis of both tumours is essential for immediate treatment to improve prognosis. It would be interesting to clarify whether there is a common mechanism between the co-occurrence of GIST and lymphoma. [ABSTRACT FROM AUTHOR]