Patient Characteristics and Overall Treatment Response
A total of 155 patients were enrolled in this study, with a median age of 62 years (range, 44 to 82 years), and were divided into training (109 patients) and validation cohorts (46 patients). The median follow-up was 47.0 months (95% CI, 44.6 to 49.5 months) in the training cohort and 34.7 months (95% CI, 32.2 to 37.2 months) in the validation cohort. By December 2021, 49 patients (34 from the training cohort and 15 from the validation cohort) were still alive. Eighty-three(76.1%) patients in the training cohort experienced relapse, of which 44 (53.0%) suffered a local recurrence (LR), 31 (37.3%) suffered a regional recurrence (RR), and 22 (26.5%) suffered distant metastases (DMs). The training cohort’s 1-, 2-, and 3-year OS rates were 75.0%, 51.0%, and 37.8%, respectively. Forty-three (43.9%) patients were classified as active responders, and 55 (56.1%) patients as non-responders. In the validation cohort, a total of 36 (78.3%) patients developed a recurrence, of which 18 (50.0%) experienced a LR, 14 (38.9%) experienced a RR, and 13 (36.1%) experienced DMs. The validation cohort’s 1-, 2-, and 3-year OS rates were 70.0%, 41.3%, and 31.8%, respectively, with 16 (40.0%) and 24 (60.0%) patients being classified as responders and non-responders, respectively.
Interim Analysis
The presence of stenosis was observed in 42 (38.5%) of 109 patients in the training cohort and 21 (45.7%) of 46 patients in the validation cohort, respectively. As for ulceration, 20 (18.3%) of 109 patients and 10 (21.7%) of 46 patients were observed in the training and validation cohorts, respectively. In the training cohort, excellent remission (ER), good remission (GR), and minor remission (MR) were achieved by 59 (54.1%), 30 (27.5%), and 20 (18.3%) patients, respectively (Fig. 2A). In the validation cohort, the rates were 22 of 46 (47.8%) for ER, 14 of 46 (30.4%) for GR, and 10 of 46 (21.7%) for MR (Fig. 2B). The interim response evaluation revealed that, after CRT, tumor thickness was significantly reduced in the training cohort (14.9 ± 5.5 mm vs. 9.9 ± 3.6 mm, P < 0.001) (Fig. 2C) and also in the validation cohort (16.3 ± 6.5 mm vs. 10.1 ± 3.7 mm, P < 0.001) (Fig. 2D). However, no obvious changes of lumen involvement were observed during the treatment in these two cohorts (training cohort, 0.74 ± 0.23 vs. 0.72 ± 0.24, P = 0.152; validation cohort, 0.83 ± 0.20 vs. 0.80 ± 0.21, P = 0.384) (Figs. 2E, F).
Prognostic Significance Of The Interim Analysis
Clinical factors related to responders are shown in Table 1. A significant correlation was found between the interim response evaluation outcomes and responders. Residual tumor thickness (8.56 ± 3.15 vs. 11.13 ± 3.60mm, P < 0.001), reduction of tumor thickness (0.38 ± 0.17 vs. 0.26 ± 0.16, P < 0.001), tumor length (4.72 ± 2.25 vs. 5.66 ± 2.16cm, P = 0.037), and lumen involvement at baseline (0.70 ± 0.24 vs. 0.79 ± 0.22, P = 0.043) and during treatment (0.68 ± 0.23 vs. 0.77 vs. 0.23, P = 0.045) were significantly different between responders and non-responders (Table 1). No significant correlations were found for stenosis (P = 0.100), ulceration (P = 0.862), baseline tumor thickness (P = 0.323) and tumor remission (P = 0.082) (Table 1). Responders had a larger proportion of ER than non-responders; however, the p-value was not significant. We then combined tumor remission with spatial luminal involvement (SLI) during treatment; ER and SLI tumors achieved higher predictive values for responders, with a specificity of 83.6% (46/55, 95%CI 70.7–91.8%, P = 0.001) (Table 1).
Table 1
Clinical evaluation outcomes by EUS with biopsies of responders and non-responders†
Variables | Responders (42) | Non-responders (56) | P |
Stenosis | | | 0.100 |
Yes | 14 | 27 | |
No | 29 | 28 | |
Ulceration | | | 0.862 |
Yes | 8 | 11 | |
No | 35 | 44 | |
Tumor length (mm) | 4.72 ± 2.25 | 5.66 ± 2.16 | 0.037 |
Tumor thickness (mm) | | | |
Baseline | 14.37 ± 5.59 | 15.44 ± 4.99 | 0.323 |
Residual | 8.56 ± 3.15 | 11.13 ± 3.60 | < 0.001 |
Reduction | 0.38 ± 0.17 | 0.26 ± 0.16 | < 0.001 |
Lumen involvement | | | |
Baseline | 0.70 ± 0.24 | 0.79 ± 0.22 | 0.043 |
Residual | 0.68 ± 0.23 | 0.77 ± 0.23 | 0.045 |
Biopsies | | | 0.082 |
Minor | 5 | 14 | |
Good | 10 | 17 | |
Excellent | 28 | 24 | |
Combination analysis | | | 0.001 |
ER and SLI | 20 | 9 | |
Others | 23 | 46 | |
†98 patients were included in the analysis of the training cohort; the remaining 11 patients were not included due to the short follow-up time. Abbreviations: ER, excellent remission; SLI, spatial luminal involvement. |
Independent Prognostic Factors For Pfs And Os
Survival data for the primary cohort were analyzed. Patients with ER or SLI tended to have improved PFS and OS compared to those without, although the difference was not significant (PFS, P = 0.058, 0.086; OS, P = 0.11, 0.12). However, patients with both ER and SLI had significantly better PFS and OS than those with ER alone, SLI alone, or neither (PFS, P = 0.004; OS, P = 0.002) (Fig. 3). Table 2 shows the results of the univariate Cox regression analysis. Stenosis, baseline T, baseline N, TNM stage, tumor length, and reduction in tumor thickness were associated with PFS and OS. Residual tumor thickness was only associated with OS (P = 0.042), but not with PFS (P = 0.109). Variables with a p-value < 0.05 in the univariate analysis were selected for the multivariate Cox regression analysis. Since the TNM stage combines the depth of tumor infiltration and the status of lymph node metastasis, we only included the TNM stage for further analysis. Finally, TNM stage (P = 0.001, 0.002), tumor length (P = 0.013, 0.008), reduction in tumor thickness (P = 0.004, 0.004), and ER/SLI (P = 0.041, P = 0.031) were found to be independent prognostic factors for PFS and OS (Table 3).
Table 2
Patient and tumor characteristics and univariate Cox regression of variables associated with PFS and OS
Variables | N (%) | PFS | | OS |
HR (95% CI) | P value | | HR (95% CI) | P value |
Age,median,y | 62(44–82) | 0.875(0.568–1.346) | 0.543 | | 1.042(0.662–1.642) | 0.857 |
Male sex | 90(82.6) | 1.502(0.830–2.717) | 0.178 | | 1.366(0.735–2.536) | 0.324 |
Smoke | 79(72.5) | 1.083(0.787–1.491) | 0.625 | | 0.998(0.694–1.437) | 0.992 |
T1-3 vs T4 | 85(78.0) | 1.822(1.099–3.022) | 0.020 | | 1.864(1.114–3.119) | 0.018 |
N0-1 vs N2-3 | 71(65.1) | 1.813(1.163–2.826) | 0.009 | | 2.005(1.262–3.186) | 0.003 |
TNM category | | | 0.002 | | | 0.003 |
I/II | 23(21.1) | 1.0 | | | 1.0 | |
III | 55(50.5) | 1.758(0.958–3.225) | 0.069 | | 2.237(1.114–4.491) | 0.024 |
IV | 31(28.4) | 3.156(1.643–6.064) | 0.001 | | 3.552(1.704–7.406) | 0.001 |
Ulceration | 20(18.3) | 1.203(0.697–2.076) | 0.507 | | 1.172(0.654-2.100) | 0.593 |
Stenosis | 42(38.5) | 1.594(1.029–2.467) | 0.037 | | 1.640(1.036–2.596) | 0.035 |
Tumor length > 5.0 cm | 50(45.9) | 1.622(1.051–2.502) | 0.029 | | 1.769(1.122–2.789) | 0.014 |
Tumor thickness (mm) | | | | | | |
Baseline ≥ 15 mm | 52(47.7) | 0.999(0.649–1.538) | 0.997 | | 1.117(0.709–1.760) | 0.633 |
Residual ≥ 10 mm | 49(45.0) | 1.426(0.924–2.201) | 0.109 | | 1.608(1.017–2.543) | 0.042 |
Reduction ≥ 0.36 | 51(46.8) | 0.557(0.359–0.865) | 0.009 | | 0.548(0.345–0.872) | 0.011 |
Lumen involvement | | | | | | |
Baseline ≥ 0.67 | 55(50.5) | 1.307(0.848–2.013) | 0.225 | | 1.264(0.803–1.990) | 0.312 |
Residual ≥ 0.67 | 51(46.8) | 1.458(0.946–2.248) | 0.088 | | 1.437(0.909–2.273) | 0.121 |
Tumor remission | | | 0.123 | | | 0.230 |
Minor | 20(18.3) | 1.0 | | | 1.0 | |
Good | 30(27.5) | 0.577(0.333-1.000) | 0.050 | | 0.616(0.344–1.103) | 0.103 |
Excellent | 59(54.1) | 0.795(0.434–1.454) | 0.456 | | 0.829(0.440–1.563) | 0.562 |
Combination analysis | | | | | | |
ER and SLI | 32(29.4) | 1.0 | | | 1.0 | |
others | 77(70.6) | 0.480(0.289–0.798) | 0.005 | | 0.428(0.245–0.748) | 0.003 |
Abbreviations: PFS, progression free survival; OS, overall survival; HR, hazard ratios; CI, confidence intervals; ER, excellent remission; SLI, spatial luminal involvement. |
Table 3
Multivariable Cox regression of variables associated with PFS and OS
Variables | PFS | | OS |
HR (95% CI) | P | | HR (95% CI) | P |
Stenosis | 1.508(0.964–2.359) | 0.072 | | 1.528(0.948–2.463) | 0.081 |
TNM category | | 0.001 | | | 0.002 |
I/II | 1.0 | | | 1.0 | |
III | 1.124(0.596–2.121) | 0.717 | | 1.504(0.728–3.106) | 0.271 |
IV | 3.009(1.530–5.918) | 0.001 | | 3.588(1.646–7.821) | 0.001 |
Tumor length | 1.770(1.128–2.780) | 0.013 | | 1.903(1.185–3.057) | 0.008 |
Tumor thickness | | | | | |
Residual > 10mm | | | | 0.838(0.478–1.470) | 0.538 |
Reduction > 0.36 | 0.491(0.301-0.800) | 0.004 | | 0.456(0.265–0.782) | 0.004 |
Others vs ER and SLI | 0.576(0.339–0.977) | 0.041 | | 0.479(0.245–0.934) | 0.031 |
Abbreviations: PFS, progression free survival; OS, overall survival; HR, hazard ratios; CI, confidence intervals; ER, excellent remission; SLI, spatial luminal involvement. |
Development And Validation Of Nomograms
Using the four prognostic markers that were demonstrated to be significantly independent in the multivariate Cox regression analysis, we constructed two nomograms to predict the 1-, 2-, and 3-year PFS and OS for ESCC patients who received dCRT (Fig. 4A, 5A). The possibilities of PFS and OS at 1, 2 and 3 years were estimated by adding the points of each item on the nomogram.
We mainly evaluated the predictability of the nomograms from three aspects: discrimination, calibration, and clinical effectiveness. Our nomograms yielded a C-index of 0.713 (95% CI 0.663–0.762) in predicting PFS and 0.711 (95% CI 0.657–0.765) in predicting OS. Additionally, the time-dependent ROC curves of the nomograms demonstrated a better discrimination of PFS and OS than those of the TNM stage at almost all time points in the follow-up, in both the training (Figs. 4B, 5B) and validation cohorts (Figs. 4C, 5C). The calibration curves for 1-, 2-, and 3-year OS and PFS revealed an excellent agreement between the observed survival rates and the predictions of the nomograms, implying the superior accuracy of the predictions (Figs. 4D, E, 5D, E). Besides, diagrams of the DCA showed that the net benefits of our nomograms were significantly higher than those of the extreme curves, and more than those of the TNM stage in predicting PFS (Figs. 4F, G) and OS (Fig. 5F, G).
Risk stratification for PFS and OS
We summed up the prognostic scores of all independent risk markers in the nomogram models, and the total points ranged from 0–264 for PFS and from 0–273 for OS in the training cohort. Using the median value as a cutoff, we further separated patients into high- (PFS, ≥ 133.5; OS, ≥ 156.5) and low-risk (PFS, < 133.5; OS, < 156.5) groups. We found that the PFS and OS in both groups significantly differed (PFS, HR = 3.097, 95% CI 1.960–4.893, P < 0.001; OS, HR = 3.279, 95% CI 2.007–5.356, P < 0.001) (Fig. 6A, B), which was consistent with the results obtained in the validation group (PFS, HR = 4.977, 95% CI 2.247–11.025, P < 0.001; OS, HR = 5.719, 95% CI 2.356–13.886, P < 0.001) (Fig. 6C, D).