Prognostic Predictors of Gastrointestinal Stromal Tumors: a Multi-institutional Analysis of 102 Patients with Definition of a Prognostic Index

Aims: The aim of this study is to identify prognostic factors influencing survival in patients with gastrointestinal stromal tumors (GISTs) and to identify a mathematical model that can predict lifetime expectation.

Methods: One hundred and two patients with GISTs, were followed retrospectively for a median period of 32 months (from 1 to 82 months). Complete follow-up data were available in 72 cases. All tumors were surgically resected and examined by conventional light microscopy, immunohistochemistry and image analysis. The tumors' location, size, histologic characteristics, immunophenotype, proliferative activity index (assessed by proliferating cell nuclear antigen (PCNA) and Ki-67 immunoreactivity) and the apoptotic markers bcl-2 and bax, were considered as potential prognostic factors and were correlated with patient survival.

Results: Tumor size >8 cm (p<0.03), presence of necrosis (p<0.02), number of mitoses >5/10 HPF (p<0.01), metastasis (p<0.001), and PCNA index >10% (p<0.004) were significant predictors of poor survival. Bcl-2 protein (p<0.0007) was a favorable prognostic indicator. If all tumors were treated as of uncertain malignant potential, the following mathematic model named GISTs Prognostic Index (GPI), could be formed by the linear regression technique: GPI exp=(49.6 months-Status of metastasis x 22.9185-Size in cm x 0.6801+bcl-2 expression% x 0.2569) (r(2)=0.67) (Prob>F=0.0001).

Conclusions: Tumors' size, necrosis, mitoses, metastasis and PCNA index are independent poor prognosticators, while bcl-2 protein is associated with favorable prognosis. An interesting equation for survival in patient with GISTs has been reported.