Adjuvant imatinib mesylate prolongs recurrence-free survival (RFS) after resection
of localised primary gastrointestinal stromal tumours (GIST). We aimed to develop
a nomogram to predict RFS after surgery in the absence of adjuvant therapy to help
guide patient selection for adjuvant imatinib therapy.
A nomogram to predict RFS based on tumour size (cm), location (stomach, small intestine,
colon/rectum, or other), and mitotic index (<5 or > or =5 mitoses per 50 high-power
fields) was developed from 127 patients treated at Memorial Sloan-Kettering Cancer
Center (MSKCC), New York, NY, USA. The nomogram was tested in patients from the Spanish
Group for Research on Sarcomas (GEIS; n=212) and the Mayo Clinic, Rochester, MN, USA
(Mayo; n=148). The nomogram was assessed by calculating concordance probabilities
and testing calibration of predicted RFS with observed RFS. Concordance probabilities
were also compared with those of three commonly used staging systems.
The nomogram had a concordance probability of 0.78 (SE 0.02) in the MSKCC dataset,
and 0.76 (0.03) and 0.80 (0.02) in the validation cohorts. Nomogram predictions were
well calibrated. Inclusion of tyrosine kinase mutation status in the nomogram did
not improve its discriminatory ability. Concordance probabilities of the nomogram
were better than those of the two NIH staging systems (0.76 [0.03] vs 0.70 [0.04,
p=0.04] and 0.66 [0.04, p=0.01] in the GEIS validation cohort; 0.80 [0.02] vs 0.74
[0.02, p=0.04] and 0.78 [0.02, p=0.05] in the Mayo cohort) and similar to those of
the AFIP-Miettinen staging system (0.76 [0.03] vs 0.73 [0.004, p=0.28] in the GEIS
cohort; 0.80 [0.02] vs 0.76 [0.003, p=0.09] in the Mayo cohort). Nomogram predictions
of RFS seemed better calibrated than predictions made with the AFIP-Miettinen system.
The nomogram accurately predicts RFS after resection of localised primary GIST and
could be used to select patients for adjuvant imatinib therapy.