GSTs develop from the Cajal mesenchymal cells or their common stem cells and are potentially malignant. They could occur at any age but mainly in the middle aged and senior people, exhibit similar incidence in men and women [14], which agrees with our study.
In this study, the tumor size in high-risk group was larger than the other two groups. Using the low-risk group as a reference, multivariable analysis indicated that the longest diameter was the independent risk factors for high-risk GSTs. Previous studies [15, 16] indicate a correlation between larger tumor size and worse prognosis for patients, which was consistent with our results. The characteristics of tumor rapid growth is indicative of malignant tumors. The tumor size in low-risk group was similar to that of moderate-risk group. Therefore, tumor size could not be used to differentiate low- from moderate-risk GSTs.
In the present study, we found that the incidence of ulceration increased with increasing risk classification, with significant difference different groups. Meanwhile, Ulceration was the independent risk factors for high-risk GSTs. We speculated that GSTs with higher risk classification were probably more invasive and easily destroyed gastric mucosa. The incidence of feeding artery and vascular-like enhancement in high-risk group was about 3 times higher than the other two groups. Research by Xu et al. [17] also showed that feeding artery and vascular-like enhancement were more likely to occur in high-risk GSTs. Neovascularization is an important step in tumor metastasis and invasion for malignant tumors. A relatively larger tumor in high-risk group likely accounted for this result, because larger tumors would need more neovascularization to provide nutrition for tumor growth.
The necrosis rate (92.9%) of tumors in high-risk group was significantly higher than that of the low- and moderate-risk groups. Grazzini et al. [11] also found that necrosis rate of tumor was 99% in high-risk group. High-risk tumors grew at a faster rate and disproportionately to the relatively slow growth rate of neovascularization, leading to ischemic necrosis. Previous studies [17–18] reported that the degree of enhancement in the venous phase reduced as risk stratification increasing, in consistency with results of the present study. A possible explanation for this outcome is that the growth rate of neovascularization in the moderate- and high-risk groups was lower than the growth rate of the tumor, result in relatively few contrast agents to enter the tumor. In addition, the high-risk tumor is easily to myxoid change and ischemic necrosis, which resulted in reducing CT value in venous phase. A previous study by Jumniensuk et al. [19] showed that GISTs with myxoid change were likely to exhibit recurrence and metastasis.
Growth patterns of high-risk lesions were mainly mixed and exophytic patterns, rarely endophytic, consistent with our results [15, 20]. Most GSTs in high-risk group were of irregular morphology (78.6%). On the contrary, GSTs with regular morphology was seen more often in low- and moderate-risk groups. A study by Neill et al. [21] also showed that irregular morphology or lobulation was an independent risk factor for GSTs recurrence and metastasis, consistent with our study. A probable explanation for this result is that tumor cell heterogeneity increases concomitantly with increasing tumor aggressiveness, contributing to faster growth rate in more aggressive tumor parts. Fat positive signs around lesion was more common in high-risk group than the other groups. Kim et al. [22] also found that GSTs with mesenteric fat infiltration were likely to be of high risk. This clinical outcome might be explained by that the high ability of highly aggressive tumors to infiltrate the surrounding tissue. Alternatively, a larger tumor volume in high-risk group might compress the surrounding blood vessels more easily, resulting in adipose tissue edema.
To the best of our knowledge at present, there were few nomograms model of CT features for prediction of risk stratification for GSTs. In the present study, using low-risk group as a reference, multivariate logistic regression analysis showed that location, ulceration, longest diameter and vascular-like enhancement were independent risk factors of high-risk GSTs. With moderate-risk group as a reference, morphology, necrosis and feeding artery were independent predictors of high-risk GSTs. Two nomogram model were both successfully established to predict the high-risk GSTs and had good prediction efficiency. Logistic regression equation can graphically be present with nomogram. It is convenient and simple to utilize nomogram for risk of GSTs prediction through simple addition operation, with practical value for clinical evaluation of patients.
There were some limitations in the study. First, a retrospective study led to selection bias. Possible non-uniformity in the CT scanner and parameters, injection speed and doses of contrast agent might also impact results. Second, the study failed to perform three-dimensional reconstruction of CT images because lake of thin-slice CT images, which might also impact results.