Frequent occurrence of low grade cases among metastatic gastrointestinal stromal tumours

Gastrointestinal stromal tumours (GISTs) are uncommon mesenchymal neoplasms. Some metastasise, whereas others remain asymptomatic for years, but it is difficult to distinguish between them histologically. This report analyses the characteristics of seven metastasising GISTs and compares clinicopathological parameters of the metastatic and non-metastatic groups.

Histology revealed typical GIST features with spindle, epithelioid, or mixed appearance. All seven cases were positive for vimentin, five for neurone specific enolase, six for c-kit, four for S-100, three for PGP-9.5, three for CD-34 and synaptophysin, but all were negative for cytokeratin, neurofilament, chromogranin A, and desmin. Four showed a focal reaction for smooth muscle actin. Three of the tumours were GI, and two each were GII and GIII. The Ki-67 index varied from 4% to 44%, the three GI cases had 4%, 10%, and 16%. Tumours from the metastatic GIST group were significantly larger than those from the non-metastatic group.

Three cases exhibited bland, GI histological features with moderate or low proliferative activity. Among the c-kit positive metastasising stromal tumours, some were low grade, with moderate or low mitotic and Ki-67 indices, emphasising the necessity to develop a reliable grading system for GIST to predict clinical behaviour, the importance of careful analysis of "benign looking" tumours, and the key role of c-kit status in identifying patients who could benefit from treatment with STI-571. Larger tumours had a higher chance of metastasising, and only the size of the primary tumour played a role in predicting metastatic potential.