Gastrointestinal stromal tumours in patients with other-type cancer: a mere coincidence or an etiological association? A study of 97 GIST cases.

Gastrointestinal stromal tumours (GIST) occur mostly as sporadic solitary lesions involving the tubular GI tract and are only rarely associated with other benign or malignant neoplasms or occur as part of a multi-neoplastic disease as in the setting of Carney's triad and von Recklinghausen's disease. We analysed a total of 97 cases of surgically resected GIST looking for various types of associated non-GIST malignancies. 18 cases (18.6 %) were identified. There were 12 women and 6 men aged 43 to 87, average age 71.7 years. 12 GISTs were located in the stomach, four in the small intestine, and one each in the duodenum and the vermiform appendix. Associated malignancies (mostly carcinomas) were gastrointestinal/pancreatic (9), gynaecological (3), mammary (2), renal (1), prostatic (1), pulmonary (2) and haematolymphoid (2) in origin. Most GISTs (16/18) represented benign or low-risk lesions (innocent bystanders) detected during evaluation for the known cancer, either during staging, intra-operatively or on follow-up. Two women (43 and 72 years old) with large malignant GISTs (10.5 and 12 cm), one of them with two simultaneous hepatic metastases resected at the same time as the primary GIST, developed infiltrating ductal mammary carcinoma and were alive and well 75 and 95 months postoperatively, respectively. Furthermore, one of them developed endometrial carcinoma. We concluded that GISTs are not uncommonly encountered in cancer-patients during staging, intraoperatively or on follow-up and should be considered in the differential diagnosis of newly detected focal lesions to avoid their misinterpretation as metastasis from the known malignancy with consequently false therapeutic decisions.