Large gastrointestinal stromal tumor and advanced adenocarcinoma in the rectum coexistent with an incidental prostate carcinoma: A case report

INTRODUCTION: Gastrointestinal stromal tumors (GISTs) are the leading mesenchymal neoplasia in the gastrointestinal tract, but GIST arising from the rectum is rare. When a secondary neoplasia coexists in the vicinity of a rectal GIST, more aggressive treatment strategies may be needed to cure the diseases. PRESENTATION OF CASE: We herein describe a 76-year-old man with a large gastrointestinal stromal tumor along with an advanced adenocarcinoma in the rectum that coexisted with prostate carcinoma. Preoperative examination revealed an advanced adenocarcinoma of the upper rectum and a large pelvic mass suggestive of a GIST or a neuroendocrine tumor arising from the anterior wall of the lower rectum. To eradicate the tumor, total pelvic exenteration with ureterocutaneous fistula was carried out after obtaining written informed consent. Immuhistochemical studies revealed the concurrence of an advanced rectal cancer (T3, N1, M0) and a malignant GIST (c-kit-positive, CD34-positive, vimentin-positive, and CAM5.2-negative), and an incidental prostatic acinar adenocarcinoma. The patient was given adjuvant chemotherapy with imatinib and remains disease-free as of 12 months after surgery. DISCUSSION: A PubMed search for the case of coexistence of GIST with two other malignancies revealed only four cases, making this very rare condition. CONCLUSION: Radical surgery with perioperative adjuvant chemotherapy using tyrosine kinase inhibitors is the choice for treatment of large GISTs with a malignant potential. Our report suggests that aggressive surgical approach would be feasible, when a secondary tumor is present near the GIST.