The surgical principles for managing SMTs include laparoscopic resection for small tumors and avoidance of tumor rupture, wedge resection, and complete resection of gross disease and adherent organs [9
]. A wide resection of the full thickness of the gastric wall with adequate margins is a satisfactory procedure for malignant gastric SMTs, while mass enucleation may be sufficient for benign gastric SMTs [12
]. The preoperative prediction of malignant potential in patients with gastric SMTs plays an important role in deciding on the operative method. However, it is difficult to diagnose whether a tumor is malignant preoperatively; the definitive diagnosis of gastric SMTs is possible only with pathological confirmation.
EUS is used widely in the evaluation of gastric SMTs. Unfortunately, EUS is not yet reliable enough for differentiating between benign and malignant SMTs. Palazzo et al. [14
] reported that the three most predictive EUS features for malignancy were irregular margins, cystic spaces, and lymph nodes with a malignant pattern. They found that the presence of at least one of these criteria had a sensitivity of 91%, specificity of 88%, positive predictive value of 83%, and negative predictive value of 94% for potential malignancy. We found that EUS has a high diagnostic sensitivity for the malignant potential of SMT, in agreement with previous studies [8
]. However, EUS had a low specificity and positive predictive value for the diagnosis of malignant SMTs in our study. Therefore, we need better preoperative predictors for malignant SMTs to establish the surgical plan.
In this study, three factors predicted malignant SMTs in the multivariate analysis. The first was age. Rabin et al. [15
] found a significant correlation between age and malignant potential and reported that the younger the patient, the higher the incidence of malignancy. Contrary to their results, the mean age was higher in the malignant group in our series. No similar data regarding age as a predictor of malignant SMTs were found when reviewing other reports.
Second, mucosal ulceration is a common feature of gastric SMTs. Miettinen et al. [16
] reported that the presence of ulceration has no predictive value or prognostic significance, although it may be related to tumor size. In another study, Miettinen et al. [17
] demonstrated that ulceration was common in all histologic subtypes but, nevertheless, was an adverse prognostic factor, probably because of its consistent presence in malignant SMTs. In contrast to their result, we found that tumor ulceration predicted malignant SMTs.
Third, tumor size was another predictor of malignant SMTs in our series. Tumor size is an easily applicable morphologic criterion for predicting tumor behavior. In some studies, tumor size > 6 cm has been suggested as a threshold value for malignancy [18
]. Miettinen et al. [17
] suggested that 5 cm was a threshold value for malignant SMTs, despite an unpredictable, but low, frequency of unexpected progressive disease among patients with relatively small tumors and low mitotic activity, although this frequency does not exceed 2 to 3%. Hsu et al. [20
] also reported that tumor size ≥ 10 cm carried both a higher risk of recurrence and worse survival in SMTs. We used ROC curves to determine the optimal cut-off value for size to distinguish malignant and benign tumors. Examining different threshold values, the most relevant for malignant SMTs prediction were 4.05 and 6.40 cm. A cut-off value of 4.05 cm had a sensitivity of 49.6%, specificity of 86.2%, positive predictive value of 72.5%, and negative predictive value of 69.9%. When the cut-off value was increased to 6.40 cm, the specificity reached 99.4% and the positive predictive value was 96.8%. We propose 4 cm as the threshold value.
In conclusion, malignant SMTs were significantly associated with age, the presence of central ulceration, and tumor size. We suggest that a tumor size of 4 cm be selected as the threshold value for malignant SMTs. If an ulcerated SMT is bigger than 4 cm, we recommend a wide wedge resection of the full thickness of the gastric wall, or gastrectomy with adequate margins, because it has high potential for malignancy.