Predicting the risk of interval distant metastases in patients with esophageal squamous cell carcinoma undergoing chemoradiotherapy

Background: This study was conducted to identify risk factors for distant interval metastases (IM) in patients with esophageal squamous cell carcinoma (ESCC) who underwent chemoradiotherapy (CRT). Methods: We retrospectively reviewed the clinical records of 358 patients with ESCC treated with CRT between 2006 and 2017. Distant IM were defined as systemic metastases developing during or shortly after CRT and identified during the restaging work-up period. A risk prediction nomogram for distant IM was developed based on independent pretreatment risk factors identified using multivariable logistic regression analysis. Results: Distant IM occurred in 26 (7.3%) patients and had a significant adverse impact on survival (median survival: 8.7 months). The most common site of distant IM was the lung (n = 9), followed by non-regional lymph nodes (n = 8) and the bone (n = 8). Multivariable logistic regression analysis revealed that high baseline tumor SUVmax values were independently associated with an increased risk of distant IM (odds ratio [OR] = 1.059, p = 0.019), whereas older age was an independent protective factor (OR = 0.946, p = 0.032). A nomogram based on age, tumor SUVmax, tumor length, and the chemotherapy regimen showed a good predictive performance (c-statistic = 0.761), which was internally validated using 200 bias-corrected bootstrap replicates (c-statistic = 0.71). Conclusion: Distant IM were identified in 7.3% of patients with ESCC undergoing CRT. The nomogram described in our study may prove useful to predict the risk of distant IM in this patient group.