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Conditional disease-free survival after surgical resection of gastrointestinal stromal tumors: a multi-institutional analysis of 502 patients.

IMPORTANCE
Gastrointestinal stromal tumors (GISTs) are the most commonly diagnosed mesenchymal tumors of the gastrointestinal tract. The risk of recurrence following surgical resection of GISTs is typically reported from the date of surgery. However, disease-free survival (DFS) over time is dynamic and changes based on disease-free time already accumulated following surgery.


OBJECTIVES
To assess the comparative performance of established GIST recurrence risk prognostic scoring systems and to characterize conditional DFS following surgical resection of GISTs.


DESIGN, SETTING, AND PARTICIPANTS
A retrospective cohort study of 502 patients who underwent surgery for a primary, nonmetastatic GIST between January 1, 1998, and December 31, 2012, at 7 major academic cancer centers in the United States and Canada.


MAIN OUTCOMES AND MEASURES
Disease-free survival of the patients was classified according to 5 prognostic scoring systems, including the National Institutes of Health criteria, modified National Institutes of Health criteria, Memorial Sloan Kettering Cancer Center GIST nomogram, and American Joint Committee on Cancer gastric and nongastric categories. The concordance index (also known as the C statistic or the area under the receiver operating curve) of established GIST recurrence risk prognostic scoring systems. Conditional DFS estimates were calculated.


RESULTS
Overall 1-year, 3-year, and 5-year DFS following resection of GISTs was 95%, 83%, and 74%, respectively. All the prognostic scoring systems had fair prognostic ability. For all tumor sites, the American Joint Committee on Cancer gastric category demonstrated the best discrimination (C = 0.79). Using conditional DFS, the probability of remaining disease free for an additional 3 years given that a patient was disease free at 1 year, 3 years, and 5 years was 82%, 89%, and 92%, respectively. Patients with the highest initial recurrence risk demonstrated the greatest increase in conditional survival as time elapsed.


CONCLUSIONS AND RELEVANCE
Conditional DFS improves over time following resection of GISTs. This is valuable information about long-term prognosis to communicate to patients who are disease free after a period following surgery.