3.4  Diagnostic performance of each modality in the evaluation of tumor response to chemoradiation using GEE
Tables 3 to 5 show the diagnostic performance of between the 3 modalities and ypT stages of 110 tumors. Among a total of 110 patients, 34 patients showed good tumor response by both the endoscopy and combination modality (Fig. 4). Of these 34 patients, 23 were confirmed as true absence of tumor by histopathologic analysis, which meant that the PPV of endoscopy for ypT0 was 67.65% (95% confidence interval [CI]: 51.92–83.37) by using the GEE. On the contrary, 11 of 30 patients with good tumor response by MR tumor response were confirmed as ypT0 by histopathologic analysis (PPV 36.67%, 95% CI: 19.42–53.91). Both endoscopy and combination modality showed the highest values in sensitivity (79.31%), PPV (67.65%), NPV (92.11%), and accuracy (84.55%) and theses values showed significantly higher diagnostic performances than those of mrTRG for the prediction of ypT0 (Table 3). When evaluating ypT0-1 by using 3 modalities, there was no significant difference at distinguishing ypT0–1 from ypT2–4 (PPV of endoscopy: 52.94% (95% CI: 26.16–69.72), PPV of mrTRG: 43.33% (95% CI: 25.60–61.07), PPV of combination modality: 46.67% (95% CI: 32.09–61.24), respectively, P = .330). However, combination modality showed significantly higher sensitivity than that of mrTRG (70.00% vs 43.33%, P = .001) (Table 4). When comparing 3 modalities for the prediction of ypT0-2, all modalities showed relatively high diagnostic performance in differentiating ypT0-2 from ypT3-4 (PPV of endoscopy: 85.29% [95% CI: 73.39–97.20], PPV of mrTRG: 80.00% [95% CI: 65.69–94.31], PPV of combination modality: 82.22% [95% CI: 71.05–93.39], respectively, P = .688). In addition, sensitivity, NPV, and accuracy showed significantly higher values in combination modality than those of mrTRG (sensitivity: 56.92% vs 36.92%, P ≤ .001, NPV: 56.92% vs 48.75%, P = .003, accuracy: 67.27% vs 57.27%, P = .003, respectively) (Table 5).
Figure 4  Response assessment with endoscopy; red scar with telangiectasia (black arrow) and white scar (white arrow) shows typical sign of clinical complete response after chemoradiation therapy.
Table 3  Diagnostic performance power predicting ypT0.
Table 4  Diagnostic performance power predicting ypT0-1.
Table 5  Diagnostic performance power predicting ypT0-2.