Gastrointestinal stromal tumors (GISTs) have unique immunohistochemical and molecular genetic features that set them apart from leiomyomas, leiomyosarcomas, and schwannomas. Although recurrence of GIST usually tends to develop locally or in the liver, rectal GIST reoccur predominantly at the original site of the tumor. We describe a rare
case of rectal GIST with multiple liver metastases. We carried out immunohistochemical staining for p53 protein, proliferating cell nuclear antigen (PCNA), integrins, and interleukin-1 receptor type I (IL-1RI) in order to investigate the degree of malignancy of this neoplasm in addition to the immunohistochemical analyses that were necessary for diagnosing GIST. Histologically, the rectal tumor was classified as an uncommitted type of rectal GIST with multiple liver metastases. Positive immunostaining for PCNA, alpha6 integrin subunit, and IL-1RI was found in both the rectal and hepatic tumors. The patients with a rectal GIST may have an increased risk of liver metastasis and a poor prognosis independent of the size of the tumor.