A modification of NIH consensus criteria to better distinguish the highly lethal subset of primary localized gastrointestinal stromal tumors: a subdivision of the original high-risk group on the basis of outcome.

BACKGROUND: By reappraising the National Institutes of Health (NIH) consensus criteria, we worked on establishing a modified scheme to identify highly lethal gastrointestinal stromal tumors (GISTs), which have an imperative demand for sequencing analysis to assess the suitability of an adjuvant imatinib trial.
METHODS: Clinicopathologic features, including NIH and modified schemes, were retrospectively analyzed for 289 patients with localized GISTs. We combined the very low/low-risk GISTs into a single "risk level I" group (<or=5 cm, <5/50 high power fields [HPFs]) and redesignated the intermediate-risk GISTs as "risk level II" (either <5 cm, 6 to 10/50 HPFs or 5 to 10 cm, <5/50 HPFs). The GISTs of "risk level IV" group were >5 cm and >10/50 HPF, with the rest of high-risk GISTs defined as "risk level III."
RESULTS: The cumulative 5-year rate of disease-specific survival (DSS) for all 289 patients was 82%, and the DSS rates for patients with GISTs classified as risk levels I to IV were 100%, 96%, 67%, and 25% at 5 years, respectively. The prognostic differences were striking between the risk level II and III groups (P < .0001) and between the risk level III and IV groups (P = .0002). The higher risk level of our scheme represented the strongest independent adverse factor (risk ratio [RR] = 11.299 for risk level III; RR = 33.815 for risk level IV; P < .0001), followed by mixed/epithelioid histology (RR = 2.837, P = .003) and older age (>or=70 years, RR = 1.955, P = .044).
CONCLUSIONS: Remarkable prognostic heterogeneity exists in the high-risk category of the NIH scheme, which is not as effective as the modified criteria in identifying highly lethal GISTs that we classified as risk level IV.