Detecting Interval Distant Metastases With 18F-FDG PET/CT After Neoadjuvant Chemoradiotherapy for Locally Advanced Esophageal Cancer.

PURPOSE: Patients with esophageal cancer can develop distant metastases between the start of neoadjuvant chemoradiotherapy (nCRT) and planned surgery (ie, interval distant metastases). 18F-FDG PET/CT restaging after nCRT detects interval distant metastases in ~8% of patients. This study aimed to identify patients for whom 18F-FDG PET/CT restaging after nCRT could be omitted using an existing prediction model predicting for interval distant metastases or by using clinical stage groups. PATIENTS AND METHODS: Patients with locally advanced esophageal cancer who underwent baseline and restaging 18F-FDG PET/CT, nCRT, and were planned for esophagectomy between 2017 and 2021 were eligible for inclusion in this retrospective study. The primary outcome was the existing model's external performance (ie, discrimination and calibration) for predicting interval distant metastases. The existing model predictors included tumor length, cN status, squamous cell carcinoma histology, and baseline SUVmax. The secondary outcome determined the clinical stage groups (AJCC/UICC eighth edition) for adenocarcinoma and squamous cell carcinoma for which the incidence of interval distant metastases was <10%. RESULTS: In total, 127 patients were included, of whom 17 patients developed interval distant metastases (13%; 95% confidence interval [CI], 8%-21%) and 9 patients were deemed to have false-positive lesions on 18F-FDG PET/CT (7%; 95% CI, 2%-11%). Applying the existing model to this cohort yielded a discriminatory c-statistic of 0.56 (95% CI, 0.40-0.72). The calibration of the existing model was poor (ie, mostly underestimating the actual risk). The incidence of true-positive versus false-positive interval distant metastases for patients with clinical stage II disease was 5% versus 0%; clinical stage III, 14% versus 8%; and clinical stage IVa, 22% versus 9%. CONCLUSIONS: The existing prediction model cannot reliably identify patients at risk for developing interval distant metastases after nCRT for esophageal cancer. Omission of 18F-FDG PET/CT restaging after nCRT could be considered in patients with clinical stage II esophageal cancer.

Severe lymphopenia acquired during chemoradiotherapy for esophageal cancer: Incidence and external validation of a prediction model.

BACKGROUND: The incidence of grade 4 lymphopenia in patients treated with chemoradiotherapy (CRT) according to Chemoradiotherapy for Oesophageal cancer followed by Surgery Study (CROSS) regimen is unclear. The primary aim was to determine the incidence of grade 4 lymphopenia during CROSS for esophageal cancer. Secondary aims were to externally validate a prediction model for grade 4 lymphopenia and compare overall survival between patients with and without grade 4 lymphopenia. METHODS: Patients who underwent CRT for esophageal cancer between 2014 and 2019 were eligible for inclusion. Patients with a planned radiation dose of 41.4 Gy (CROSS) or 50.4 Gy ("extended-CROSS") and concurrent carboplatin and paclitaxel were included. The primary outcome was the incidence of grade 4 lymphopenia during CRT defined according to Common Terminology Criteria for Adverse Events version 5.0 (i.e. lymphocyte count nadir < 0.2 µL). The secondary outcome measures were the prediction model's external performance (i.e. discrimination and calibration). Overall survival for patients with versus without grade 4 lymphopenia was compared using Kaplan-Meier analysis. RESULTS: A total of 219 patients were included of whom 176 patients (80%) underwent CROSS and 43 patients (20%) extended-CROSS. The incidence of grade 4 lymphopenia was 11% in CROSS and 33% in extended-CROSS (p < 0.001). External discrimination yielded a c-statistic of 0.80 (95% confidence interval: 0.70-0.89). External calibration of the model was poor in CROSS but fair in extended-CROSS. Adjusted calibration using intercept correction (adjusted for the lower a-priori risk for grade 4 lymphopenia in CROSS) showed fair agreement between the observed and predicted risk for grade 4 lymphopenia. Median overall survival in patients with versus without grade 4 lymphopenia was 12.7 versus 42.5 months (p = 0.045). CONCLUSION: The incidence of grade 4 lymphopenia is significantly higher in esophageal cancer patients receiving extended-CROSS compared to those receiving CROSS. The prediction model demonstrated good external performance in the setting of the CROSS-regimen and could be used to identify patients at high-risk for grade 4 lymphopenia who might be eligible for lymphopenia-mitigating strategies.