Background and objectives: Gastrointestinal stromal tumor (GIST) is mesenchymal neoplasms of the gastrointestinal tract, which express CD117, a c-kit proto-oncogene protein and show gain of function mutation of c-kit gene. Apart from the presence of metastasis, the criteria to differentiate benign and malignant GISTs are not well-defined. Although a variety of prognostic factors have been investigated, no method has yet proven sufficient to enable reliable determination of malignancy in all cases. This study was planned to risk stratify the GIST cases with respect to the various clinicopathological features and to identify prognostic factors in GIST.
Materials and methods: n histological and immunohistochemical analysis, 121 cases of GIST were identified. MIB-1 (Ki-67) labeling index (LI) was performed in 60 cases. Follow-up data was available for 93 patients. A P < 0.05 was taken as significant.
Results: Larger tumor size, high mitotic activity and Ki-67 LI of >10% were identified as significant predictors of disease-free survival in univariate analysis (P < 0.0001). Other factors of statistically significant value were a high cellularity (P < 0.0027), nuclear pleomorphism (P = 0.0002), epithelioid cell type (P = 0.0098), presence of tumor necrosis (P < 0.01), presence of skeinoid fibers (P = 0.042), S-100 negativity (P = 0.025). Extra-gastrointestinal GIST and metastasis were more frequently associated with progressive disease (PD) as compared with GIST (P < 0.0004), (P < 0.0001). On multivariate analysis size (P = 0.0025), Ki-67 labeling index (P = 0.0186) and mitotic count (P = 0.0375) emerged as independent prognostic predictors of PD.
Conclusion: This study suggests that GIST in Asian population may have a different phenotype with some predilection to nodal metastasis. Of all the features studied, tumor size and mitotic index are the best prognosticators in GIST with the addition of Ki-67 LI, wherever available.