JOURNAL OF CANCER & ALLIED SPECIALTIES 1 CASE REPORT J Cancer Allied Spec 2018;4(2):6 PRIMARY GASTROINTESTINAL STROMAL TUMOUR OF PROSTATE: A CASE REPORT OF A RARE TUMOUR M. Arshad Irshad Khalil, Nouman Khan, Azfar Ali, Khurram Mir Department of Surgical Oncology, Shaukat Khanum Memorial Cancer Hospital and Research Centre, Lahore, Pakistan Received: 30 January 2018 / Accepted: 25 June 2018 Abstract A 70-year-old gentleman underwent prostatectomy for bladder outlet obstruction due to enlarged prostate and was found to have primary extragastrointestinal stromal tumour (EGIST). He has been started on imatinib therapy and is presently on follow-up. Prostatic EGIST should be one of the differential diagnoses in patients with enlarged prostate with normal prostate-specifc antigen levels. Key words: Prostate, gastrointestinal stromal tumour, PSA Correspondence: Dr. M. Arshad Irshad Khalil, Department of Surgical Oncology, Shaukat Khanum Memorial Cancer Hospital and Research Centre, Lahore, Pakistan. Email: arshadkmcite@gmail.com Introduction Gastrointestinal stromal tumours (GIST) are common in the digestive tract. They have their origin in the pacemaker cells specifc to the GI tract. Since similar cells are known to exist in the prostate, such tumours can very rarely be found to arise from this site also. They can be recognised based on histology using specifc immunohistochemical stains and can be treated by immunotherapy, surgery or combination of the two methods. [1,2] In this case report, a primary prostatic extra-GIST (EGIST) is presented, which has been treated with imatinib (IM) and is considered for surgery. Case Report A 70-year-old male patient had undergone transvesical prostatectomy in September 2017, for complaints of severe lower urinary tract symptoms i.e., hesitancy, poor stream and sense of incomplete voiding for the past 5 months. As per patient’s record pre-operative examination revealed an enlarged frm nodular prostate. His pre-operative prostate-specifc antigen (PSA) level was 2.67 ng/ml. Histopathologic examination of specimen from revealed features consistent with GIST. Immunohistochemical staining showed the following reactivity: • CD117 diffuse positive. • DOG-1 diffuse positive. • CD34 positive. • Desmin negative. • ASMA negative. He was further worked up with colonoscopy and upper GI endoscopy to fnd any primary tumour in the lower GI tract. No gross abnormality was found on these examinations. He was accepted in Shaukat Khanum Memorial Cancer Hospital and Research Centre through walk-in clinic and presented to the Department of Uro-oncology. Histopathology was reviewed at our institution as per policy. It showed that on gross examination, there were multiple irregular fragments of greyish-brown tissue, measuring 11.0 cm × 10.0 cm × 5.0 cm. On sectioning, greyish-brown and haemorrhagic tissue was noted. The whole specimen was submitted in three blocks. Microscopic examination shows neoplastic lesion, which was composed of fascicles of spindle cells. These neoplastic cells contain a moderate amount of eosinophilic cytoplasm with oval-to-elongated nuclei and inconspicuous nucleoli. At places, cytoplasmic vacuolisation is also appreciable. The mitotic count was 2–3/50 high-power felds (HPF) [Figure 1]. No normal prostatic tissue was seen.