Predictors of Malignant Behaviour in Gastrointestinal Stromal Tumours: A Clinicopathological Study of 34 Cases.

Objective: The clinicopathological features of gastrointestinal (GI) stromal tumours were analysed to find out the features that influence prognosis in these neoplasms. Design: Retrospective study. Setting: University Hospital, Spain. Subjects: Review of clinical records and analysis of a series of GI stromal tumours classified in three groups: benign = 7 leiomyomas, malignant or potentially malignant = 16 combined smooth muscle-neural tumours, and 2 miscellaneous, and definitely malignant = 1 leiomyosarcoma and 8 gastrointestinal autonomic nerve tumours. Main outcome measures: Electron microscopy and immunohistochemical staining for vimentin, smooth muscle actin, muscle specific actin, desmin, S-100 protein, neuronal specific enolase, chromogranin A, synaptophysin, CD34, CD117 (c-kit), Bcl-2, and Ki-67. Results: We found significant differences (p < 0.0001) between the median (P25, P75) size of tumours in the benign group 2.0 (1.2, 3.5) and in the potentially 7.5 (4.0, 13.0) and definitely 5.0 (4.0, 6.5) malignant groups. The percentage of mitoses was lower (p = 0.003) in the benign group 0.4 (0.5) than in the other groups 2.0 (1.0, 5.0). Immunoreactivity for CD117 in leiomyomas was an unexpected finding; this showed a different staining pattern from the diffuse and homogeneous staining in GI stromal tumours. In addition, the MIB-1 proliferation index differentiated (p = 0.002) between the benign group 1.5 (1.0, 2.5) and the other two groups 7.0 (3.0, 11.0). Conclusions: These findings support the idea that GI stromal tumours form a heterogeneous group of neoplasms in which large size, presence of necrosis, and a high proliferative index (mitotic rate or MIB-1 index, or both) are good predictors of malignant behaviour. [ABSTRACT FROM AUTHOR]