Cancer biology of small gastrointestinal stromal tumors (<2 cm): What is the risk of malignancy?

Abstract

Introduction: The identification of small (<2 cm) gastrointestinal stromal tumors (GISTs) is increasingly recognized. The malignancy potential is not absent. However, data on risk is scarce. The aim was to review the existing data on perceived risk of small GISTs in population-based studies.

Methods: A combined review of small GISTs (<2 cm) in a population-based dataset compared with a systematic review of available population-based studies.

Results: About one in every four (27%) patient has a small GIST, of which 79% were incidental in presentation, and all had a low-risk mitoses index (<5/hpf). The small GISTs had C-KIT mutations in exon 11 or 9 (66%), none had mutation in PDGFRA, and 33% were non-KIT/PDGFRA. The rate of small GISTs increased for each advancing age group. None of the small GISTs had a recurrence nor were there any GIST-specific deaths during follow-up. A "small GIST" rate at one-fourth of all GISTs reported was corroborated in other population-based studies from Norway, Iceland and Korea. Common to studies reporting mitosis index were an almost universal finding of very low-risk in small GISTs, with very few recurrences and an excellent long-term survival reported to 95-100% in several series.

Discussion: One in every four GIST diagnosed is a small GIST (<2 cm). Small GISTs are increasingly found with advanced age and have an overall excellent prognosis. Defining true risk-features for proper surveillance and treatment strategy is needed in order to avoid over- and under-treatment.

Keywords: Cancer biology; Epidemiology; GIST; Malignancy; Mutation; Risk.