LAUSR

Diagnosis of pelvic gastrointestinal stromal tumors (GISTs) can be challenging because of their nonspecific presentation and similarity to gynecological neoplasms. In this series, we describe the clinicopathological features of 20 GIST cases: 18 patients presented with pelvic mass and/or abdominal pain concerning gynecological disease; 2 patients presented with a posterior rectovaginal mass or an anorectal mass. Total abdominal hysterectomy and/or salpingo-oophorectomy (unilateral or bilateral) were performed in 13 cases. Gross and histological examination revealed that the ovary/ovaries were involved in three cases, the uterus in two cases, the vagina in two cases and the broad ligament in one case. Immunohistochemically, all tumors (20/20, 100%) were diffusely immunoreactive for c-KIT. The tumor cells were also diffusely positive for DOG-1 (10/10, 100%) and displayed focal to diffuse positivity for CD34 (11/12, 92%). Desmin was focally and weakly expressed in 1 of the 14 tested tumors (1/14, 7%), whereas 2 of 8 tumors (2/8, 25%) showed focal SMA positivity. At the molecular level, 7 of 8 (87.5%) GISTs with molecular analysis contained c-KIT mutations with the second and third c-KIT mutations detected in some recurrent tumors. In addition to c-KIT mutation, a pathogenic RB1 mutation was detected in two cases. We extensively discussed these cases focusing on their differential diagnosis described by the submitting pathologists during consultation. Our study emphasizes the importance of precision diagnosis of GISTs. Alertness to this entity in unusual locations, in combination with clinical history, morphological features as well as immunophenotype, is crucial in leading to a definitive classification.