Gastrointestinal stromal tumors (GISTs) with remarkable cystic change: a specific subtype of GISTs with relatively indolent behaviors and favorable prognoses

PURPOSE: Gastrointestinal stromal tumors (GISTs) are typically solid neoplasms with small cystic change detected occasionally but in rare instances may present predominantly as cystic lesions. The histopathologic features and prognoses of cystic GISTs (cGISTs) are poorly understood. METHODS: We herein reviewed 20 cGISTs resected or consulted in our institution from January 1, 2003 to December 31, 2014. RESULTS: Of the 20 patients included, the mean age was 61 years and the male-to-female ratio was 9:11. The original locations were the stomach (n = 10, 50%), the small intestine (n = 9, 45%) and the omentum (n = 1, 5%). Indistinct diagnosis or misdiagnosis was established in 15 cases based only on preoperative radiology. Grossly, the cystic component made up the bulk of masses and was filled by dark bloody fluid and necrotic debris in 18 cases. Microscopically, cyst wall was composed of neoplastic spindle (n = 14, 70%)/epithelioid cells (n = 6, 30%) and collagenous fiber, with necrotic debris and granulation tissue lining on the inner surface. cGISTs resembled their solid counterparts in terms of morphology and immunohistology but demonstrated fewer malignant parameters. c-kit or PDGFRα mutations were detected in eleven cases with the remaining being wild type for these two mutations. Although classified as intermediate or high (3 and 17, respectively) risk of recurrence according to modified National Institute of Health criterion, most patients with cGISTs experienced long-term recurrence-free survival without adjuvant imatinib. CONCLUSIONS: Cystic GISTs is a relatively indolent subset of GISTs with favorable prognoses and adjuvant imatinib should be a prudent consideration.