Gastrointestinal stromal tumors in the appendix - A clinicopathologic and immunohistochemical study of four cases

Mesenchymal tumors of the appendix are very rare, and specific stromal tumo rs (i.e., gastrointestinal stromal tumors, GISTs) have not been reported in this location to date. Four GISTs were identified in the review of primary mesenchymal tumors of the appendix from the files of the Aimed Forces Inst itute of Pathology from 1970 to 1998. There were also one benign schwannoma , one diffuse neurofibroma with neurofibromatosis 1, one leiomyosarcoma in a child with HIV infection, and one inflammatory fibroid polyp. The four ap pendiceal GISTs occurred in adult males 56-72 years of age (mean 63 years). Two tumors occurred in patients who had surgery for appendicitis-like symp toms: one was an incidental finding during surgery for a malignant gastric epithelioid GIST and one was an incidental autopsy finding. Only one of the two appendices operated for symptoms had acute inflammation, and a polypoi d GIST projected outward from the proximal part of appendix. Three tumors w ere partially obliterating nodules, eccentrically expanding the appendiceal wall. All four were spindle cell tumors, and three of them contained extra cellular collagen globules (skeinoid fibers); none had atypia or mitotic ac tivity (<1/50 high power fields). Immunohistochemically, two tumors studied were positive for CD117 (KIT), and two were positive for CD34. The tumors were negative for a-smooth muscle actin and S-100 protein. Follow-up reveal ed death from cardiovascular disease in one case (4 years after appendectom y) and liver failure because of malignant gastric epithelioid GIST metastat ic to liver in another case 15 years after the appendectomy. This report do cuments the rare occurrence of CD117-positive GISTs as primary appendiceal tumors.